1.5.20

1. Added setting for tinted illumination saturation (Settings -> Star Styles)
2. Added setting for star colors (Settings -> Star Styles)
3. Added setting for game controller actions (Settings -> Game Controller)
4. Added setting for custom flight mode (Camera Control -> Flight Mode)
5. Show error message from core

Core updates:

1. Update galaxy and globular rendering
2. Performance improvements
3. Avoid crashing on bad models

celestiamobile/Celestia@00e9562
CelestiaProject/CelestiaContent@d9580cd
celestiamobile/CelestiaLocalization@e99b51a