v3.3.0: OpenTracks

Breaking changes:
- Pictures are now stored in app-private storage (do not show up other picture apps)
  NOTE: Pictures taking with previous version cannot be shown
- Localization for Spanish (Latin America) only works on Android 7.0 or later

Changes:
- Import/Export via Storage Access Framework (avoids READ/WRITE_EXTERNAL_STORAGE permission)

Developer:
- Cleaned internal data structures
- Use separate icons/app names for debug version