This reworks the implementation of the applet/containment configuration
so that it is more optimized for the mobile experience and fixes lateral
navigation (between categories).
Changes:
- Always show a list of category modules (switching from the navigation
tab bar) in order to support more modules at once
- Split the wallpaper and containment switching view into two modules
- Add a close button at the top
- Add an animation when the window opens and closes
- Refactor the code so that it is clear which files are imported by the
shell, and which are implementation details
