NEW: in msct_image: pad_image function doesn't use isct_c3d anymore, and is callable in command line
NEW: in msct_image: pad_image function doesn't use isct_c3d anymore, and is callable in command line

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox