v3.0.0: OpenTracks

First release of OpenTracks (i.e., hard fork from MyTracks)

Changes:
- Rebranded from MyTracks to OpenTracks
- Added Bluetooth LE heart rate sensor
- Removed all features requiring Internet access
- Removed Google Maps integration
- Removed use of Google Play services
- Removed ANT+ sensors
- Removed Bluetooth classic sensors
- Removed Protobuf
- Removed calorie estimation and activity estimation
- Removed MyTracks Service API (i.e., no integration with other apps)