Miscellaneous clean-ups.

- Fix the way the name field is initialized for various objects.
- Mark variables which are constant as "const".
- Use GFX_rotate(const quaternion &) to precompute sine/cosine.
- Use TStack::loadMatrix() to more directly load a matrix onto
  transformation stack.
- Use vec3(const vec4 &) to simplify conversion out of homogeneous
  space and into 3D.
- Remove MAX_*_MATRIX definitions from SDK/common/gfx.h since they're
  no longer used.
- Miscellaneous clean-up in MD5 module.
- Initialize SOUNDBUFFER::bid, MD5WEIGHT::location, MD5WEIGHT::normal,
  and MD5WEIGHT::tangent to eliminate need of memset().
- Update comments to more accurately reflect current state of the code.
Make “float” the default type for vector, matrix, and quaternion class templates.

Do a little more clean up on GFX_unproject().