Implement drivers (AppStream)

[donadigo]

Implements drivers and fixes #12.

After discussion on the Slack channel I decided to give AppStream implementation of drivers a go. We no longer depend on any Ubuntu / Debian specific code. Everything is based on AppStream and PackageKit, however scanning modaliases on the system is pretty much a Vala version of the UbuntuDrivers component. For more details about the code and it's design, look into the diff, I left some explanation for each driver related method.

Note that currently there is no AppStream data to test this branch with and this is kind of a problem since this feature is being asked by lots of people. So how did I test it?
The way to test this is to fool AppStream that some components are drivers. All of the compiled data is stored in /usr/share/app-info/yaml/pantheon_xenial-main_amd64.yml.gz file. Open this file with archive manager (with admin), and edit the .yml file inside of it. Choose some component and change it's Type field from desktop-app to driver. Next you will need a supported modalias by your system. These can be found by e.g: executing ubuntu-drivers debug and choosing one of the modalias strings. After that you can paste this under the Provides field:

modaliases:
  - your_modalias

and save the file.

Sorry if this is really complicated but this is the only way I found to test this. Perhaps Matthias knows a better way.

[Conan-Kudo]

@donadigo Is there a way we could have both backends supported, and have a build-time option to use one or the other?

[donadigo]

@Conan-Kudo yes, we could use conditional compiling here.

[Philip-Scott]

Is this PR still valid? Or does your other PR for the drivers supersede this?

[donadigo]

@Philip-Scott yes, this PR is still valid. We're waiting on having all the drivers available as AppStream data, that's why this PR is blocked and cannot be merged now.

[decathorpe]

Could you rebase this against current master?
I think this change would make driver support work on fedora, too, since drivers already work with gnome-software / packagekit / appstream.

[jeremypw]

@donadigo Converting to draft as has conflicts and no recent activity. Please feel free to close or request review as desired.

[danirabbit]

Gonna close this since there hasn't been movement in a couple years