Merge branch 'personal/cordes/gradient-manipulating' into bug-15065-GradientVectorLengthCompensation

Conflicts:
Modules/DiffusionImaging/DiffusionCore/IODataStructures/DiffusionWeightedImages/mitkDiffusionImage.txx
Plugins/org.mitk.gui.qt.diffusionimaging/src/internal/QmitkPreprocessingView.cpp
Plugins/org.mitk.gui.qt.diffusionimaging/src/internal/QmitkPreprocessingView.h