Support for displacement textures on mapmodels.

[SniperGoth]

We already have support for these types of textures, which can really make cool effects with, on the octree, and decals. Feels like having them on mapmodels could be useful for certain situations which would either take too much time, or not be worth the effort to make with only the octrees, like, as an example, a big sphere that surrounds the entire map as if it was some sort of force field.

And of course, don't forget that the manipulation of a model's UV maps by the 3d artist could help with giving things a unique look, too.