Add support for gapps stock package

Users can chose between the three gapps packages in settings (full, mini and stock).
The default one is the full package.
GappsUpdater: use maintenance version number
Treat date as a number
UpdateFragment: reworked layout

Shows info on the current rom and gapps.
The lennon image has been reduced a little.
Don't merge before these other changes:
https://gerrit.paranoidandroid.co/#/c/3544/
https://gerrit.paranoidandroid.co/#/c/3545/
https://gerrit.paranoidandroid.co/#/c/3550/