Show NMEA output

[barbeau]

To provide better debugging info we should provide a display for raw NMEA data using http://developer.android.com/reference/android/location/GpsStatus.NmeaListener.html.

This should be added discretely, since most users probably won't benefit from this. Maybe in open space under the Sky view?

[barbeau]

GpsStatus.NmeaListener is deprecated as of Android 7.0 API Level 24 - OnNmeaMessageListener should be used instead:
https://developer.android.com/reference/android/location/OnNmeaMessageListener.html

[barbeau]

To get this into the app without waiting on a UI overhaul, I'm adding the ability to dump the NMEA output to the Log, which is visible via Android Monitor (e.g., via Android Studio). This will work for pre-Android 7.0 and Android 7.0 and up.