Built out star system functionality, scaled values

Most of the (near) star and related planets generation code was moved into the starSystem object. Changed the way entities are added to the global scene for a star system's objects by moving them to a shared entity array.

All system objects' radii are now set in kilometers, and image sizing for texture generation of the relevant physical maps now have to be scaled down for drawing on the scene. Mass is now set in kilograms also. Units have been added to the toString() methods for stars and planets.

The camera placement and planet display distance is based on the current system's star size, so that the star's surface will show at the left side of the screen consistently, with the (currently single) planet visible in the center of the frame. The glow from a near star was modified to give more transition now that the camera is so much closer to the star body.

The texture generation functions for spheres (both solid and gradient) were modified to accept imageSize directly, to reflect the change in realistic values to scaled projection values of the physical bodies.
Removed debug code and fixed a typo