Optimizations to pre-post transform matrix

[bsupnik]

This bug is a place-holder to put in optimizations to the pre-post transform matrices that will improve the quality of the output OBJ8.

• When a data block is loc-only key framed OR its rotation key frames are static (all rotations have the same orientation) we want the post-animation coordinate system of the bone wrapped around the data block to be pre-rotation, so that we can avoid writing the rotation as ananimation prefix.

(This optimizes nested animations by avoiding intermediate rotations and their associated static translations.)

• When an armature bone's rotation is static (unchanging) we want the post-animation matrix of the armature to contain only the translation.

(This is the same case as above, but for armatures.)

• When an armature bone is loc+rot key-framed, we want our post-animation coordinate system to be around the tail of the armature. (I'm not sure there's any other possible implementation.)

(This optimizes out a static translation per armature rotation, at least in theory.

[tngreene]

Now that we have made several improvements to the animation algorithm, is this still relevant?

[bsupnik]

I think the last part for armatures is still not done and could be done in a future exporter.