Use Cloud Firestore

[WillieCubed]

Resolves #1

• [x] Update app to use Cloud Firestore as data source
• [ ] ~Add script to migrate data~
• [ ] ~Add dialog to encourage users update to new version~
• [x] Revamp User management with Firestore backend

[WillieCubed]

Going to merge as the build is failing do to external dependency issue.

[WillieCubed]

Cloud Firestore