Implemented Skeletal Animation Blending

This work was directly integrated into the Animation object with some additional bookkeeping added to the Bone object.  

Concerns:
- Because Animation is used for non-skeletal animation, this results in more special case code being added.
- There might be a more flexible way to blend multiple Quaternions but the current way is correct and is easy to iteratively apply.
- The API for handling animations is very bare bones.  I'm hoping that somebody with more experience can fill it out.

Anyhow, it works!  

Enjoy, 
Michael