Many changes ... again.

I must learn to use small commits.
This commit will not work. Changes:

- Bone deformation in shader use a 4x4 affine transformation matrix
- Correct physics environment deinitialization and tweaked gravity
- `XMTRANSFORM` does not use a `XMMATRIX` for its storage anymore (it
does not store the rotation origin)
- Converted `PMX::Bone` into an interface and created two classes:
`detail::RootBone` and `detail::BoneImpl`
- Debug rendering for joints
- Fixed the wierd rendering error by disabling the OM stage for the
geometry shader