The previous animation blending system had some flows. The
AnimationHandler was owned by the model which was incorrect, since it's
possible to change models during an animation sequence. The
AnimationHandler is now owned by the item, ensuring there is only one
per character instance.
We now ignore animation change requests for one frame. This is because
the scripts often cause an animation change, and request another one the
very next frame. This used to cause issues because we were blending the
latest animation with the previous one which was only active for one
frame, causing a discontinuity. This new solution is kind of a hack.
Hopefully it is good enough and there is no need to implement animation
blending for more than two animations at once.
