Expose physical coords

Expose on render view proxy the SetPhysicalToWorldMatrix method (via a new PhysicalToWorldMatrix property), which will be available on vtkRenderWindow after the corresponding VTK change is merged.

Update some representations to be aware of already-existing coordinate system api on underlying actors, and expose a new representation proxy property (called CoordinateSystem) allowing users to place objects in World or Physical coords.

Update vtkPVLODActor and vtkPVLODVolume to be aware that actors can be in non-world coordinate systems, and to recompute bounds when that is the case.