Add Firebase Crashlytics for crash reporting

While legacy stable kmapro releases have analytics on the Google Play Console, Google recommends [Firebase Crashlytics](https://firebase.google.com/docs/crash/) for crash reporting.
This requires a `google-services.json` file for gradle builds. A sanitized version intended for developers/Debug variant is checked into the repo, and is associated with an appliction ID `com.tavultesoft.kmapro.debug`. The one for `com.tavultesoft.kmapro` releaeses will go on the CI servers.

Breaking change: Consuming apps of KMEA will be responsible for including the Firebase dependencies. At the moment, only kmapro has been updated.
TBD: Registering KMSamples and the Test Harness with Firebase for their own `google.services.json` file.

- Log addKeyboard as an analytic event 
- Update kmapro build.sh script to allow debug-only variant
- Add info to history.md and README.md
- Add Gradle setting so CI server can use production `google-services.json` file
- Temporarily add a menu button to force a crash. This is engineering code that will be removed once analytics in a Release build is confirmed.