Store a Ptr with the collision object
Reimplement heightfield collision loading
Handle object activation
Add the start of a Nif Bullet loader
Fix physics object rotation
Load collision shapes from Nif files
Don't add collisions for placeable objects
Make the model name lower case before loading

Helps avoid loading duplicate collision shapes because of different
casings being specified.
Add methods to get a scaled copy of collision shapes

Scaled copies aren't actually generated yet.