Adds basic glTF import (although right now it only imports back
positions) and fixes support for more of the vertex data that's
available to us. The MDL file isn't written back out yet either, it only
displays in the viewport.
Physis gained skeleton and deform file read support, so we can use that
and extract these directly from the game (without help of the Havok SDK
like TexTools.) The racial deform is still slightly off, but this is
still a pretty big milestone.
