New Entities Features

Adds...
* Stretchability, true Dimensions
* Angular Velocity
* Visibility
* registration point - now you can rotate or place entities based on an location within the entity space, this allows for easier editing and rotating
* natural dimensions
* new UI for "natural dimensions"
* fixes the crash in butterflies.js

change Model to support snapping to an arbitrary registration point in it's model space instead of just the center