add AACubeShape to ShapeCollider

In prepartation for making the avatar ragdoll collide against world objects I've added an AACube shape to represent voxels in the physics engine.  An AACubeShape can collide against SphereShapes and CapsuleShapes, and have been unit tested.

Also, I've renamed the old shape-vs-voxel methods with the term "Legacy".  These are the methods that I'll be removing once I've got voxel represented in the same simulation as the avatar ragdoll.