Writing position/orientation to secondary capture files

[dgobbi]

The vtkDICOMSCGenerator class defines secondary capture very narrowly, and unlike the MR and CT generators, it does not write the Image Plane Module to the DICOM file even though this module is a very common extension to the secondary capture IODs. In fact, it's a very common workflow to read an MR/CT, perform some processing, and then write out a parametric map as secondary capture. Such a workflow should be supported by vtk-dicom.