Add extension to render debug primitives

[zuck]

The idea is to provide a simple API (maybe in the Utility library) to render native debug primitives like cubes, spheres, cones, cylinders, quads, triangles, etc.

The API should be simple enough, like the Overlay's one. The system should be able to batch for material all the primitives.

Discussion on this thread:

http://www.horde3d.org/forums/viewtopic.php?f=8&t=1906