Enable turning on / off the ICRF grid
Add textures for Callisto and Europa

Allthough, while the textures are not the best, they serve as good
place holders for now.
Convert grayscale moon to colour

GL3 does not like grayscale...
Minor parameter adjustment for solar system
Correctly draw orbital paths for planets

Ensure orbits are drawn in roughly the correct location, this means that
the celmek library is now queried for the orbital elements of the orbital
scenegraph nodes.