Stars! And various small fixes and changes

Star quad objects now make up background over a skybox, as they generally just look better.

Also changed:
- Sun now at origin
- Project starts in display mode not edit mode
- Enter key to switch between modes
- Colour menu only shows in edit mode to allow panning
- Panning restricted to ensure we don't pan past edge of stars (to avoid rendering TOO many stars too)
- Random pink flare bug fixed