v3.18.3: OpenTracks

Changes:
- KML parsing does not require order of when/gx:coords
- Track importer: reorders locations by timestamp
- Removed rendered launcher icons for Android < 8.0.0 (API 26)
  (might look slightly different, but avoid problems for reproducible builds)

Bugfix:
- Avoid crash in charts due to race condition

Developer:
- Split GPX and KML importer (removed common inheritance)