This commit integrates the segmentations infrastructure that has been
incubated in the SlicerRT project. It is a new paradigm for handling
segmentations, see slides [1] to understand the underlying concepts.

[1] https://www.slicer.org/slicerWiki/index.php/File:20160526_Segmentations.pptx

More specifically, it adds:

* vtkSegmentationCore library (only depends on VTK)

* Segmentations loadable module including:
  - EditorEffects
  - Logic
  - MRML
  - MRML displayable manager
  - Widgets

* Segment editor scripted module

Co-authored-by:
  Andras Lasso <lasso@queensu.ca>
  Adam Rankin <arankin@robarts.ca> (initial implementation round for segmentation MRML and containers)
  Kyle Sunderland <1krs1@queensu.ca> (developed vtkPlanarContourToClosedSurfaceConversionRule)
  Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>  (build infrastructure and compilation warning fixes)

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25206 3bd1e089-480b-0410-8dfb-8563597acbee