Animation system and editors refactoring

[mrDIMAS]

This PR refactors engine's approach to animation. Key changes:

• Animations now stored inside new AnimationPlayer scene node.
• Animation blending state machines now stored in new AnimationBlendingStateMachine scene node and uses animations from specified AnimationPlayer node.
• Scene::absm_container container was removed since all animation blending state machines are now stored in separate scene nodes.
• Scene::animations container was removed.
• Animation retargetting now transfers animations from one animation player to another
• ABSM resource was removed
• Animation resource was removed
• ABSM editor is refactored to work with AnimationBlendingStateMachine scene nodes instead of ABSM resources.
• Animation editor is refactored to work with AnimationPlayer scene nodes.