New UI/Picker library

[C1710]

I'm currently working on a new library (partially based on FilemojiCompat and in some way a part of it) which adds an Emoji Picker that can be integrated into an app, supporting emoji fonts/packs from different sources:

• Assets
• Downloadable fonts, specified by the app (and probably soon with another library providing a list with Blobmoji, Noto Emoji, Twemoji and maybe OpenMoji or other open source emoji fonts)
• Fonts imported from other apps
• (Not currently, but it's planned) fonts provided by other apps through FontRequests

The user can then select them through a list that can be integrated e.g. in preferences, dialogs, etc. and the library manages the selection; in total, integration will need (for a minimal configuration) ~5 lines of code plus an entry in the AndroidManifest.xml (to disable the default behavior introduced by AndroidX Emoji2, which will be required for this library)