Merge: Better & playable Chainz of Friendz on Android, and offer landscape & portrait...

Based on #1075, so ignore the first 4 commits.

@privat You will like this one.

Credits for the artwork of Friends were missing. Sam Hocevar's name still appeared in each source file because he also created the licence used by Friendz.

Manage zooming in Friendz itselt (this service may be extracted later) and clean up all reference to Mnit automatic zoom.

Still TODO:
* Saving progress using the data_store.
* Deactivate fullscreen mode, but it causes issues with Mnit inputs.
* Somehow adapt the width of the background image or content to the device aspect ratio.

Pull-Request: #1076
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>