Mobile app

[Swordfish90]

Here there an initial mobile application which exposes almost all the features of the leanback version. It also includes a few bonus points:

• Completed the migration to AndroidX
• Fix of saved states (using proper retroarch serialization)
• Added very tiny and fast shaders for lcd and crt effectsery tiny and fast shade
• Touch controls (the previous pull request can be ignored)
• Initial work towards Android 10 (basically using StorageAccessFramework for roms)
• Fix thumbnails not working
• Handling GameActivity lifecycle

Currently only the local storage provider is supported.

[ZacSweers]

Before we dive into a review of this, do you want to do a rebase? It's a large PR so reducing context loss between future rebases after a review would be helpful