Add option in Room's Eye view for camera staying in the fixed system

[cpinter]

In SlicerRT, the reference coordinate system is the patient instead of the fixed system that the IEC standard defines. This results in the linac body moving when we change table top parameters, instead of the table moving. This is fine in Slicer, because the center of any workflow is the patient. However, it would be useful to add a mode in which the camera is moved dynamically in a way that the Fixed system stays still when such transformations are applied that move it.