Slicer3:Editor Tuning 3.6.2

Ideas for improving the Editor module:

• add search to the color selector box
• pick a new default size for the color selector box (or perhaps have it remember the last size/location picked by the user)
• give the color box a 'recently used' section
• provide 'median filter'-like tool for cleaning up bad label maps
• rename 'check points' to 'undo/redo'
• implement compression (to vtk stencils) for label maps in the undo/redo stack
• integrate the per-structure-volume functionality with the crop volume module