Bring back ability to show outline in slices/othographic slices view.

Added support to vtkGeometrySliceRepresentation to show data outline, if requested.
This avoids the need to use a vtkOutlineRepresentation just to show this
simple outline.

Change-Id: Ia4346309597780925c44d248875f2b6579f9f1a9
Merge topic 'cleaner_multislice_view' into next

cc114643 Bring back ability to show outline in slices/othographic slices view.