ENH: Add TubeTK_USE_ITKV4 option
ENH: Add TubeTK_USE_ITKV4 option

When turned on, this flag will get its Insight build from ITKv4 rather than the
Slicer's version of ITK. It will also get a build of SimpleITK. All TubeTK
components will be disabled except for ImageMath. At this point, ImageMath is
also disabled pending the addition of the SimpleITK based version.

thewtex/TubeTK,KitwareMedical/TubeTK,cdeepakroy/TubeTK,LucasGandel/TubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/ITKTubeTK,KitwareMedical/TubeTK,matthieuheitz/TubeTK,KitwareMedical/ITKTubeTK,LucasGandel/TubeTK,aylward/ITKTubeTK,matthieuheitz/TubeTK,aylward/ITKTubeTK,cdeepakroy/TubeTK,LucasGandel/TubeTK,thewtex/TubeTK,aylward/ITKTubeTK,thewtex/TubeTK,sumedhasingla/TubeTK,cdeepakroy/TubeTK,KitwareMedical/TubeTK,matthieuheitz/TubeTK,thewtex/TubeTK,LucasGandel/TubeTK,aylward/ITKTubeTK,sumedhasingla/TubeTK,matthieuheitz/TubeTK,KitwareMedical/TubeTK,sumedhasingla/TubeTK,KitwareMedical/ITKTubeTK,cdeepakroy/TubeTK,sumedhasingla/TubeTK