feat(data formats supporting): excel supporting

* ability to work with Excel data (create new chart and add data to existing chart)
* some tests was added and fixed
* documentation was udated

Closes #228 #243

LICENSE

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+WORDS USED BELOW
+
+"Gapminder offline" — this software
+"Gapminder", or "we" — Stiftelsen Gapminder <http://www.gapminder.org/>
+"you" — anyone who uses "Gapminder offline"
+
+HANDLING OF YOUR DATA
+
+"Gapminder offline" does not collect or share or transmit any data provided by you. 
+By design of "Gapminder offline" all your data stays local on your computer UNLESS 
+you yourself or some third party software doesn't share it, with or without your 
+knowledge. This means, your data is secure as much as your computer is secure. 
+"Gapminder offline" doesn't make your system less secure but also doesn't 
+guarantee it is. Gapminder assumes no responsibility if your data gets lost 
+or damaged or stolen or misinterpreted.
+
+ATTRIBUTION AND CREDITING GAPMINDER
+
+By using this software, you agree that Gapminder may in no way be affiliated with 
+any research, conclusions and/or claims produced with the help of the dataset and 
+visualizations, be it our dataset or yours. The only credit we accept is the following: 
+"Gapminder developed this visualization method and software and helped us to import the data in it". 
+We also maintain our right to openly say or publish our opinion about the conclusions 
+and research that you may produce with the help of our tools.
+
+UPDATING THE SOFTWARE
+
+By using our "Gapminder offline" software you agree to update it whenever it propmpts 
+the updates are available. If the updates don't work for you for some reason you can roll back 
+to a previous version in the menu -> check for updates. But do also complain to us via Get Satisfaction 
+(https://getsatisfaction.com/gapminder/) so that we can try our best and make updates work for you.
+
+MIT LICENSE
+
+Copyright (c) 2017 Stiftelsen Gapminder <http://www.gapminder.org/>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Gapminder Tools Offline  
+
+With Gapminder Tools Offline you can show animated statistics from your own laptop!
+
+• You can use it without internet access  
+• You can visualise your own data with it or even combine it with the datasets provided (examples & instructions)  
+• The software and the datasets will update automatically when connection is available  
+• It’s free  
+
+![app screenshot](https://s3-eu-west-1.amazonaws.com/static.gapminder.org/GapminderMedia/wp-uploads/20170113171243/Gapminder-Offline-Tools.png)
+
+## Using the app
+
+Download the stable version from here http://www.gapminder.org/tools-offline/
+
+## Release routines
+1. `npm run changelog` - generates content for `CHANGELOG.md` file with changes that have happened since last release
+2. `npm version` - this one is a bit more complicated. Let's start with what it needs in order to run.
+  - `CONVENTIONAL_GITHUB_RELEASER_TOKEN` environment variable should be set up for this command:
+
+    Example: `CONVENTIONAL_GITHUB_RELEASER_TOKEN=aaaaaaaaaabbbbbbbbbbccccccccccffffffffff npm version minor`
+
+  - this command understands following parameters:
+    - `major` (having initially version **0.0.0** by applying this option it will be changed to **1.0.0**).
+
+        Example:
+        ```
+          CONVENTIONAL_GITHUB_RELEASER_TOKEN=aaaaaaaaaabbbbbbbbbbccccccccccffffffffff npm version major
+        ```
+
+    - `minor` (having initially version **0.0.0** by applying this option it will be changed to **0.1.0**)
+
+        Example:
+        ```
+          CONVENTIONAL_GITHUB_RELEASER_TOKEN=aaaaaaaaaabbbbbbbbbbccccccccccffffffffff npm version minor
+        ```
+
+    - `patch` (having initially version **0.0.0** by applying this option it will be changed to **0.0.1**)
+
+        Example:
+        ```
+          CONVENTIONAL_GITHUB_RELEASER_TOKEN=aaaaaaaaaabbbbbbbbbbccccccccccffffffffff npm version patch
+        ```
+
+    During the release process two files will be changed and pushed to github:
+      1. CHANGELOG.md - because of added history.
+      2. package.json - because of bumped version.
+
+    **Note:** `aaaaaaaaaabbbbbbbbbbccccccccccffffffffff` - is the fake token. In order to generate proper one you need to do following: [github tutorial](https://help.github.com/articles/creating-an-access-token-for-command-line-use)
+
+    **Important note:** you should merge `development` branch into `master` and **performing `npm verison` on `master`** branch according to our [gitflow](https://github.com/valor-software/valor-style-guides/tree/master/gitflow)
+
+    **Even more important note:** while generating token (using tutorial given above) you need to choose which permissions should be granted to it. For our *release purposes* you need to choose all permissions under the section `repo`
+
+## Contributing
+We use Angular 6, Electron & chrome app featuring Webpack
+
+If you want to build the app in developer mode (simple build without creating a distributive and code signing) use the following commands:
+
+Mac
+```
+npm i
+npm run electron:mac
+```
+
+Win 64 *(should be done under Win 64 environment)*
+```
+npm i
+electron:windows
+```
+
+Win 32 *(should be done under Win 32 environment)*
+```
+npm i
+npm run electron:windows32
+```
+
+Linux
+```
+npm i
+./build-dev
+```
+
+Important note! The main goal of building the app in developer mode is testing only, 
+because `auto update` functionality will be unavailable in this case. 
+
+[Read how to build the application with code signing and stuff](https://github.com/Gapminder/gapminder-offline/blob/master/docs/build.md)  
+
+[Read about auto-update functionality](https://github.com/Gapminder/gapminder-offline/blob/master/docs/auto-update.md)
+
+
+
+## License
+
+[MIT](http://markdalgleish.mit-license.org)

docs/auto-update.md

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+# Auto update functionality
+
+So, we have next kinds of `auto update`:
+
+* Manual update
+* Full update
+* Partial update
+
+### Manual update
+
+This kind of update should be applied only for major (semver) update. For example, from 0.99.0 to 1.0.0.
+
+In this case a popup with direct link to download will be opened and user should download and reinstall the app
+according to instructions. 
+
+### Full update
+
+This kind of update should be applied for minor (semver) update. For example, from 0.44.10 to 0.45.0.
+In this case all parts of the application should be updated. Auto update system will use next url for data getting: 
+
+`http://s3-eu-west-1.amazonaws.com/gapminder-offline/#version#/Gapminder Offline-#type#.zip`
+
+Where `#version#` is expected application version.
+
+`#type#` can be:
+
+* mac - MacOS
+* win64 - Windows 64 bit
+* win32 - Windows 32 bit
+* linux - Linux
+
+Parts of the application:
+
+* V8 and electron libraries
+* `gapminder offline` scripts
+* Inner DDF dataset
+
+
+### Partial (application) update
+
+This kind of update should be applied for patch (semver) updates. For example, from 0.44.10 to 0.44.11. 
+
+In this case only `gapminder offline` application data (see above) or `inner DDF dataset update` would be updated. 
+
+Auto update system will use next url for data getting: 
+
+`http://s3-eu-west-1.amazonaws.com/gapminder-offline/#version#/partial/Gapminder Offline-#type#.zip` 
+(see ‘Build’ paragraph above)
+
+### Inner DDF dataset update
+
+Inner DDF dataset would be updated if semver version of current dataset less than semver version of dataset on
+github (https://github.com/open-numbers/ddf--gapminder--systema_globalis) 
+with existing tag (https://github.com/open-numbers/ddf--gapminder--systema_globalis/archive/1.1.0.zip , for example).

docs/build.md

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+# How to build and publish Gapminder Offline
+
+## Expected software for build process provides:
+
+* `git`
+* `nodejs` >= 8.11.3 with related `npm` for all platforms
+* `NSIS` installer creator for Windows 32 and 64 bit. It can be downloaded from [here](http://nsis.sourceforge.net).
+* `signtool` from Microsoft Windows SDK 
+
+## Preparation
+
+* get an expected repository: `git clone https://github.com/Gapminder/gapminder-offline.git`
+* `npm i`
+* `cd gapminder-offline`
+
+## MacOS
+
+First of all, an appropriate certificate for the application signing is expected on your PC. See `--sign` option [here](https://github.com/Gapminder/gapminder-offline/blob/master/build-mac#L10) for more information.
+
+Use `./build-mac` to run build process. You should see next files after successful build process finishing:
+
+* `./release/Gapminder Offline-mac/Gapminder Offline-mac.zip` should be uploaded to `amazon s3 url`/gapminder-offline/`version`/.
+  This file should be used by auto updater in `full update mode`.
+* `./release/partial/Gapminder Offline-mac/Gapminder Offline-mac.zip` should be uploaded to `amazon s3 url`/gapminder-offline/`version`/partial.
+  This file should be used by auto updater in `partial update mode`.
+* `./release/Install Gapminder Offline.dmg` should be uploaded to `amazon s3 url`/gapminder-offline/`version`/.
+  This is an installation file. It should be used by a customer.
+
+## Windows 
+
+First of all, you should create `./release` and put `gapminder.pfx` certificate file into it. Make sure that appropriate `signtool` is present on `PATH` environment variable.
+So, you should be able to run `signtool.exe`.
+
+### Windows 64 bit
+
+Use `./build-win64 #password#` to run build process. You should see next files after successful build process finishing:
+
+* `.\release\Gapminder Offline-win64.zip` This kind of file should be deployed to `amazon s3 url`/gapminder-offline/`version`/ and it will be used by auto updater in `full update mode`.
+* `.\release\partial\Gapminder Offline-win64.zip`. This kind of file should be deployed to `amazon s3 url`/gapminder-offline/`version/`partial and it will be used by auto updater in `partial update mode`.
+* `.\release\Install Gapminder Offline.exe`
+  Rename this file to `Install Gapminder Offline-64.exe` and upload it to `amazon s3 url`/gapminder-offline/`version`/.
+  This is an installation file. It should be used by customer.
+
+### Windows 32 bit
+
+Use `./build-win32 #password#` to run build process. First of all, ignore please errors regarding zip archiving. Windows 32 bit has some problems with automatic archiving. 
+
+You should see next files after successful build process finishing:
+
+* `.\release\Gapminder Offline-win32`
+* `.\release\partial\Gapminder Offline-win32`
+* `.\release\Install Gapminder Offline.exe`
+  Rename this file to `Install Gapminder Offline-32.exe` and upload it to `amazon s3 url`/gapminder-offline/`version`/.
+  This is an installation file. It should be used by a customer.
+
+Now you should pack these two directories in manual mode to: 
+
+* `.\release\Gapminder Offline-win32.zip` These kind of file should be deployed to `amazon s3 url`/gapminder-offline/`version`/ and it will be used by auto updater in `full update mode`.
+* `.\release\partial\Gapminder Offline-win32.zip`. This kind of file should be deployed to `amazon s3 url`/gapminder-offline/`version/`partial and it will be used by auto updater in `partial update mode`.
+
+Note: ask #password# `gapminder.pfx` certificate file owner.
+
+## Linux
+
+Use `./build-linux` to run build process. You should see next files after successful build process finishing:
+
+* `./release/Gapminder Offline-linux/Gapminder Offline-linux.zip` should be uploaded to `amazon s3 url`/gapminder-offline/`version`/.
+  This file should be used by auto updater in `full update mode`. Also this file should be unpacked and used by a customer as distributive.
+* `./release/partial/Gapminder Offline-linux/Gapminder Offline-linux.zip` should be uploaded to `amazon s3 url`/gapminder-offline/`version`/partial.
+  This file should be used by auto updater in `partial update mode`.