ENH: Added support for oriented grid Transform

Derivative of oriented transform is not correct (RAS/LPS inversion?)
ENH: Implemented vtkOrientedGridTransform reading/writing
ENH: Added test for vtkOrientedGridTransform.

Also removed unused vtkITK transform classes (there was a conflict with existing ITK filenames).
ENH: Replaced vtkGridTransform by vtkOrientedGridTransform everywhere

Save bspline and grid displacement shift and scale to ITK transform.
Merge branch 'master' of https://github.com/Slicer/Slicer into oriented-grid-transform
COMP: Merge 'oriented-grid-transform-integ' into oriented-grid-transform

Conflicts:
	Libs/MRML/Core/vtkMRMLTransformNode.cxx
ENH: Added warp transform null-pointer checks

Initialize grid and bspline transform with valid coefficients (indicating zero displacement) to avoid throwing errors when trying to save the scene that contains uninitialized transforms.
Added more null-pointer checks for cases when the displacement field or bspline grid is not rotated.