Big metavoxel update: removed unused pieces, converted heightfields to "spanners" in order to allow arbitrary transforms, switched to 16 bit heightfields with lossless compression, some rendering improvements.

Yes, in this case, I meant "Base" as in the base layer (the layer under the splats).  I will change it to clarify.

I missed the fact that I included the members again in the derived class (forgot to remove them after factoring out the base).  I'll fix it.