Reinstate Google Analytics

[lcjohnso]

As a Zooniverse team member, I should be able to access statistics on app use (e.g., project level accounting of time spent by volunteers), and the app should record this data (in a user-anonymous way) and send to Google Analytics for access by the Zooniverse team for producing usage reports for internal use and to provide aggregated statistics for project teams.

As part of #389 (and #402 + #404), Google Analytics + Firebase were removed due to an out-of-date react-native-google-analytics-bridge dependency. Restore GA using modern library.

[lcjohnso]

Note that Analytics for Zooniverse Mobile was configured via Firebase -- login with [email protected] Google Account and see https://console.firebase.google.com/

[coryzoon]

Closing issue since all changes have been merged with master.