Collision Shapes

Adding some Shape classes for a more featureful collision system.  Right now there are three real shapes and one base class:

Shape (base class)
SphereShape
CapsuleShape
ListShape

SphereShape and CapsuleShape have some unit test coverage in .../tests/physics/src/ but ListShape is not yet to be tested.

I've started using sphere and capsules for Model collisions but this is still a work in progress.