Added first part of final collision system. Approximates complex
geometric structures using many spheres, with the positions determined
using k-means clustering with Lloyd's algorithm.
Still some problems related to the generated models being hollow (points
need to be included inside the model and not just the mesh) and
rotation/angular velocity is not supported yet.
I had to allow public access to the SculptObject's inner geometry to run
the approximation code. Right now, the approximating spheres are being
rendered instead of the asteroids themselves but that's obviously
temporary.