Readthedocs basic setup

[offtherailz]

This PR contains a sample of sphinx documentation compatible with multi-language setup on readthedocs.

The result of this PR is deployed here:
http://docs.georchestra.geo-solutions.it

Inside the sample there is already a small page dedicated to "Localize this documentation" that shows how to update translation files"

Theme

The example in the PR uses readthedocs theme, that can be customized a little following this documentation. This allows basically to do simple customization.
We tested that also the albaster theme (the sphinx default) works on read the docs.

If interested to big customization, an investigation about using different themes (like these) or doing own we need to investigate more about feasability.

ReadtheDocs setup

Here the needed configurations to setup multi-language and custom domain.

Multi language support

ReadTheDocs allow (as documented here) to publish multi-language documentation using sphinx
This is allowed by creating 1 main project and other sub-projects (configured with a different languages in readthedocs project's administrator configuration)

Then adding the project to the translations in the Translations file

Custom domain

Readthedocs supports customdomains as documented here:
Contextually to this pull request we configured the exampled to this URL:
http://docs.georchestra.geo-solutions.it

The root project and the localized sub-projects should be configured to use same domain like in this case.