Touch inputs in retrograde-tv-app

[Swordfish90]

This pull request includes temporary touch support in retrograde-app-tv which can be enabled from the flags screen.

Touch inputs are implemented as custom views that live in a separate module with no dependencies from retrograde and expose an rx interface. Layouts for gb (nes), gba (snes) and genesis are already included.

I think we should probably remove touch support in retrograde-app-tv once the mobile application is useable, but this was my best idea to test them right now.

Let me know what you think, or if you prefer to merge touch inputs directly with the mobile application.