Add DTIPrep extension

See issue #185
ENH: DTIProcess packaging system has been simplified
ENH: DTIProcess packaging system has been simplified
ENH: FiberViewerLight packaging system has been simplified
ENH: DTIAtlasFiberAnalyzer now packages on Windows
COMP: Update FFTW download and install for windows and SlicerExecutionModel version
Merge pull request #197 from booboo69500/update-DTIProcess

ENH: DTIProcess packaging system has been simplified
Merge pull request #199 from booboo69500/update-DTIAtlasFiberAnalyzer

Update dti atlas fiber analyzer
Merge pull request #196 from booboo69500/185-add-DTIPrep

Add DTIPrep extension
Merge pull request #198 from booboo69500/update-FiberViewerLight

Update fiber viewer light
Merge pull request #200 from adrienkaiser/update-DTIAtlasBuilder

COMP: Update FFTW download and install for windows and SlicerExecutionModel version