Better sky

Lots of little improvements to stars and moons

Stars are now fixed but their shine and distribution now have more varied patterns. They also have a new shader.

Moons also got a new shader with their own color but also keep with the environment colors. Orbits are now stable on their own randomly generated orbit plane instead of wobbling like rings.

Plunging into the core (planet?) or flying off system will reset the scene (jump to another system). Same as when collecting 5 orbs