Remove an unused struct
Remove an unnecessary cast
Rename nonaccum to animroot
Use a separate class to handle activator mechanics
Use a method to update an object's cell in the mechanics manager

This prevents destroying and recreating the object's character controller (and
messing up the current animation) when moving between cells.
Add a flag to specify if an animation should be playing
Set the animation state loop flag as appropriate
Remove an unnecessary class member
Only register activators that have a MWRender::Animation object
Avoid redundant string concatenations
Print when an animation event is unhandled