Merge pull request #450 from paulcm/update-LongitudinalPETCT

Changed default setting for registration and model making to active
Add CMFreg extension
Merge pull request #454 from viboen/add-CMFreg

Add CMFreg extension
Update AirwaySegmentation extension
Merge pull request #455 from PietroNardelli/update-AirwaySegmentation

Update AirwaySegmentation extension
FIX: Fixed volume rendering related memory leak.