Rendering improvements

[lawremi]

Lots of negative feedback on the textures. Ideas:

• Ores should render as overlays, with the base texture borrowed from a nearby (whitelisted?) stone.
• Overlays should be randomized, possible via rotation.
• Stone textures should smoothly transition.

[aarondandy]

I like the current look for the most part. My only complaint is that it is hard to tell the difference between diorite and diorite brick.

[lawremi]

Thanks for the feedback. I'm going to close this one for now, since people seem generally happy.