Added new morph operator (dilation and erosion) for cubes.
(Based on this vtk-filter: http://www.vtk.org/doc/nightly/html/classvtkImageDilateErode3D.html#details)
Merge pull request #134 from CognitionGuidedSurgery/new_morph_operator

Added new morph operator (dilation and erosion) for cubes.

You merge by yourself on the `experimental` branch.  `master` is the critical one after the Hackfest.