To add support for face culling for outlines, we make vtkOutlineRepresentation a
vtkGeometryRepresentationWithFaces subclass. vtkOutlineRepresentation now
overrides certain methods in vtkGeometryRepresentation to ensure that the
representation always generates outlines. Cleaning up the xml for
"OutlineRepresentation" by being the same as the "SurfaceRepresentation". It
will have a few extra properties like "Representation", "SuppressLOD", etc. that
have no effect, but the XML ends up being much cleaner.