ENH: Add iGyne extension

Description:
iGyne is an open source software for MR-Guided Interstitial Gynecologic
Brachytherapy. It enables on-time processing of the intra-operative MRI
data via a DICOM connection to the scanner followed by a multi-stage
registration of CAD models of the template and the obturator to the
patient images. This allows the virtual placement of interstitial
needles during the intervention, as well as the detection/labeling of
needles in MR images

Contributors:
Guillaume Pernelle,  Alireza Mehrtash, Lauren Barber, Nabgha Fahrat, Jan
Egger, Tobias Penzkofer, Sandy Wells, Sam Song, Xiaojun Chen, Yi Gao,
Antonio Damato, Tina Kapur, Akila Viswanathan
Merge pull request #637 from gpernelle/add-iGyne-master

ENH: Add iGyne extension
ENH: Removed TransformVisualizer extension

The feature has been moved to the Slicer core.
Merge pull request #638 from SlicerRt/update-TransformVisualizer

ENH: Removed TransformVisualizer extension