Support writing a 16bit 3D image to a single DICOM file

[thewtex]

Request from the mailing list:

When I try to save an 8bit 3D image to a single DICOM file using ITK/GDCM, it succeeds. A suitable SOP class (Multi-frame Grayscale Byte Secondary Capture Image IOD) is assigned to the DICOM image. The same code fails when the image is 16bit, though DICOM standard does seem to have a suitable SOP class (Multi-frame Grayscale Word Secondary Capture Image IOD) for the 16bit image.