Implement Materials for Greedy Mesh Generator

[CloneDeath]

We've got basic material support for the Culled mesh generator, but not the Greedy mesh generator.

If someone could implement it for the Greedy mesh generator, I'd be much appreciative, and be able to push the next version out.

[CloneDeath]

Ehhh, it's been a while, so I went ahead and pushed 1.2, since it is, strictly speaking, better than 1.1

I'd like this done for 1.3 though. And when it's done, we can actually just remove the CulledMeshGenerator, since it is strictly worse.