1.6.6

1. Support system font scaling settings in HUD
2. Fix star browser

Core updates:

1. Fix display of ly/s speed values
2. Update unit conversions

celestiamobile/Celestia@ef9c24e
CelestiaProject/CelestiaContent@27d9de3
celestiamobile/CelestiaLocalization@e7ff7d0
celestiamobile/CelestiaCore@aa3068c