Blender Git Loki

Gawain: new enum type for vertex attrib components

Motivations:
1) GLenum is too broad; tightly-defined enum just for this is safer.
2) enable a Vulkan future

New code should use these instead of GL_FLOAT etc. When all existing code has been updated to use new enum, we can drop compatibility with GLenum values.

Early work towards 10_10_10 format, more to come soon.