Changed container type to the same as in DiffusionImage

* using a Pointer to hold the variable
* adapting subsequent calls
Adapting to changed Container type
Merge branch 'bug-15945-FixContainerType' into mbi-dev-branch
Merge branch 'master' into personal/hering/mbi-dev-branch
Changed container type to the same as in DiffusionImage

* using a Pointer to hold the variable
* adapting subsequent calls
Adapting to changed Container type
Merge branch 'personal/hering/mbi-dev-branch' of mitk.org:MITK into personal/hering/mbi-dev-branch
Changed container type to the same as in DiffusionImage

* using a Pointer to hold the variable
* adapting subsequent calls
Adapting to changed Container type
Changed container type to the same as in DiffusionImage

* using a Pointer to hold the variable
* adapting subsequent calls
Allowing more complex processing in registration
Move GradientReduction filter to DiffusionCore
Add custom test for DW convert
WIP
Single shell extraction
Merge branch 'personal/hering/mbi-dev-branch' of mitk.org:MITK into personal/hering/mbi-dev-branch

Conflicts:
	Modules/DiffusionImaging/DiffusionCore/Algorithms/itkTensorImageToDiffusionImageFilter.txx
Add single shell extraction custom test
Resolved conflicts
Fix pyramid level initialization
Fix b0 initialization in tensor to dwi