ENH: Added support for oriented grid Transform

* Added a new class, vtkOrientedGridTransform, which is based on vtkGridTransform but orientation of the grid can be specified as well.
* Added test for vtkOrientedGridTransform to verify its derivative and inverse computation and equivalence with ITK displacement field transform.
* Simplified vtkMRMLGridTransform node: transform parameters are read/written into ITK transform file, no duplicate saving is done in the scene.
* Removed unused vtkITK files: itkDisplacementFieldTransform, itkEncodedTransformFileReader/Writer, as they were not used (and some of them even had the same name as existing ITK files).
* Support reading/writing of grid transform from/to nrrd, nhdr, mha, mhd, nii, nii.gz files

Resolves:
http://www.na-mic.org/Bug/view.php?id=3597
http://www.na-mic.org/Bug/view.php?id=3444

Partially resolves:
http://www.na-mic.org/Bug/view.php?id=3598