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.
The renderer can now store diffuse, normal, specular, and multi
textures. Skin textures now color with a hardcoded skin tone (to be
changed) and bone info buffers are now per-model instead of set globally
Level of detail above 0 is now loaded properly, although break for
other reasons.
This is big, as it shows we are now correctly parsing the havok XML
sidecard data and you can edit the scale of the bones in the viewport.
This also pulls in a new libxiv version, which is required to fill out
the used bones list on a Model. Right now the bone editing is incredibly
basic, and the viewport suffers from a lack of depth testing still.
