ENH: Update FiberViewerLight from r65 to r68

BUG: To perform ExperimentalUpload, EXTENSION_SUPERBUILD_BINARY_DIR needs to be defined. It was not defined anymore since we had removed include()
http://www.nitrc.org/plugins/scmsvn/viewcvs.php?view=rev&root=fvlight&revision=68
ENH: Reorganization of CMake to add find_package(git) and find_package(Subversion) in Common.cmake
ENH: Reorganization of FiberViewerLight.cmake to look for SlicerExecutionModel before ITK
http://www.nitrc.org/plugins/scmsvn/viewcvs.php?view=rev&root=fvlight&revision=67
BUG: FiberViewerLight was including  when compiled as an extension. Doing this was including some Slicer CMake files. This used to work because those Slicer CMake files were the same as the CMake files contained in FiberViewerLight. In the latest version of Slicer, those files have changed and this was creating an incompatibility.  is not included anymore to avoid those conflicts
http://www.nitrc.org/plugins/scmsvn/viewcvs.php?view=rev&root=fvlight&revision=66
Merge pull request #582 from fbudin69500/update-FiberViewerLight

ENH: Update FiberViewerLight from r65 to r68