ENH: Added vtkSegmentationCore and Segmentations MRML, module, widget…
…s, editor
Integration of the segmentations infrastructure that used to be in SlicerRT. It is a new paradigm of handling segmentations, see slides [1] to understand underlying concepts.
[1] https://www.slicer.org/slicerWiki/index.php/File:20160526_Segmentations.pptx