Remove Google Firebase

[hacklschorsch]

I'd like to have an android-activity that is FLOSS so I can include our application in F-Droid.

Cf. reflex-frp/reflex-platform#835:

Google Firebase is not very FLOSS - See for example the F-Droid Inclusion Policy which explicitly states:

We cannot build apps using proprietary tracking/analytic dependencies like Crashlytics and Firebase. Please talk to upstream about an untainted build flavor (either using a FLOSS analytics software like ACRA or by removing Non-Free dependencies completely).

Can we make including Firebase an option instead of mandatory?

[ali-abrar]

Thanks @hacklschorsch - this has long been on our todo list. What we need to figure out is a migration path that allows those who need firebase to continue to use it even though it isn't tightly bundled anymore. CC @luigy