v3.18.0: OpenTracks

Changes:
- Altitude is shown in EGM2008 (stored/exported as WGS84)

Bugfix:
- Fixed memory leak (introduced in v3.17.0)
- Charts: altitude should be in M/FT (introduced in v3.17.1)
- Charts: while recording was not correctly updated (introduced in v3.17.3)
- TrackDataHub did not account for recordingDistanceInterval (introduced in v3.17.2)

Developer:
- Disable PNG crunching (reproducible build)
- Refactored TrackImporter and optimized KMZ import
- Use LiveData for TrackReco