AnimatorController related extension menus

These are some additional menus related to the AnimatorController.

Tools/lilEditorToolbox/Cleanup Animator Controller

Detect and remove unnecessary sub-assets contained in AnimatorController.

Copy and paste menu for StateMachineBehavior

StateMachineBehaviour can be copied and pasted just like a component.

Assets/Create/BlendTree

Allows you to create BlendTree like any other asset.