Improved texture generation, added planet details

Texture generation was moved into its own series of functions, likely to expand later on depending on additional texture needs. For now, texture generation is split between solid, single-color maps, and semi gradient dual color maps.

A bunch of planet details were added, such as temperature and specific planetary type texture creation, and the material generation was cleaned up and improved. Also added are setPosition methods for whole stars and planets, and a toString() for planets.