v3.21.0: OpenTracks

Changes:
- While recording: remove idle/non-idle creation of TrackPoints
- Settings are now in separate folders
- Opening OpenTracks from notification (while recording) and pressing back opens track list
- GPX compatibilty: support <speed> for import

Bugfixes:
- Altitude and distance (from BlE sensor): only reset counters if data was actually stored
- Import without speed, requires computing speed
- BLE running sensor not connected, should not be reported as present
- BLE r