Add animation blending

Adding animation blending (new property animation blend). This is lightly tested, so looking for feedback from tests with other models and animations. Please leave comments if you see issues (and a sample project with model would be very helpful.)

Set the animation blend property to the length of time in seconds to blend between the last animation (last position of the last animation) and the new animation. From my experience, something in the range of 0.2 - 0.5 seconds works pretty well.

Before and after: