1.5.23

Core updates:

1. Added support for RTL
2. Added support for loading galaxy templates from an addon directory
3. Added a method to change asterisms in runtime
4. Removed the load fragment script commands
5. Fixed depth sorting for nebulae

Content updates:

1. Minor update to nearstars.stc
2. Remove duplicate star

celestiamobile/Celestia@fd0073f
CelestiaProject/CelestiaContent@809c3fa
celestiamobile/CelestiaLocalization@684c18b