* Use all cluster matrices to compute bound for skinned mesh.
This is far less expensive then doing per-vertex work, but it's not free, for avatars especially.
* Remove skinnedMeshBound, compute it instead.
* Compute clusterMatrices in render update, because we need them to update bounds.
* bug fix in AABox::operator+=
* added AABox::emiggen
* Avatar now has a default bound for it's skinned mesh.
* WIP: AABox tests; NEED MORE
* Model: split collision and model mesh render items.
Because ModelMeshRenderItems need special handling to update bounds for animated joints.
* Model: dynamically update the bound for rigidly bound animated meshes
* Rig: added access to geometryToRigTransform
* RenderableModelEntityItem: try to update bounds for skinned mesh to be the entity dimentions (this doesn't seem to be working)
* Geometry.cpp: removed unused bounds parameter in evalPartBounds
* ModelMeshPartPayload: bounds updating
* non-animated: use existing _localBound
* rigid bound mesh: use _localBound transformed by clusterMatrix joint transform
* fully skinned mesh: use _skinnedMeshBound provided by the application.
