Begin development on v4.0.0
Begin development on v4.0.0

Change-Id: I794f2adf56b5ac8e08217c4d4a6ac7aba96c5f4b

SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android,firebase/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,SUPERCILEX/FirebaseUI-Android,firebase/FirebaseUI-Android