In writer, add byte swapping for 4 and 8 byte pixels.
In writer, add byte swapping for 4 and 8 byte pixels.

This is to support writing float and double in the future.

dgobbi/vtk-dicom,dgobbi/vtk-dicom,dgobbi/vtk-dicom,hendradarwin/vtk-dicom,hendradarwin/vtk-dicom,hendradarwin/vtk-dicom