ENH : factorize SliceController + new method for displayStringOrientation
@pieper @jcfr as discussed this morning for the first point.
The mapping and the methods are static so an estension can do this in its setup method
vtkMRMLSliceNode::SetAxialOrientationDisplayString("XZ");
vtkMRMLSliceNode::SetSagittalOrientationDisplayString("ZY");
vtkMRMLSliceNode::SetCoronalOrientationDisplayString("XY");
and set up the mapping for all the SliceNodes.
To get an idea in which situations this mapping will be useful:
https://github.com/Punzo/SlicerAstro/blob/master/AstroDataProbe/AstroDataProbe.py#L75