Add CMFreg extension

A registration package oriented to the Dental Research community. The registration package will perform superimposition using diverse Cranio-Maxillofacial CMF areas as stable regions of reference. This package provides several modules. Mathematical operations on label maps, mask creation, matrix application and non-growing/growing registrations.

http://www.slicer.org/slicerWiki/index.php/Documentation/Nightly/Extensions/CMFreg
https://sites.google.com/a/umich.edu/dentistry-image-computing/Clinical-Applications/3d-registration---longitudinal-and-across-subjects