NEW: msct_image: if the image to crop if smaller than the square mask : image symmetric padding to fit the mask
NEW: msct_image: if the image to crop if smaller than the square mask : image symmetric padding to fit the mask

Former-commit-id: f5d5d46f699d6edbfd335a7e5f686cee0d992c29
Former-commit-id: 840744e7b97c10d9b1478dc5a75d6078a726c70e
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox