Investigate implementing Firebase-UI equivalent controls across the board

[fenix-hub]

Lists already exist, though only for Realtime Database; try to see if it's possible to swap backend for Firestore as well (make them interchangeable through an interface if possible).

[WolfgangSenff]

@BearDooks / @fenix-hub - we should investigate building a generic login control here that can just be dropped in and configured and make it so people can just automatically add it to their games very easily.

[WolfgangSenff]

Transferring to Firebase-UI.