OPT: sct_maths: can now accept number or image
OPT: sct_maths: can now accept number or image

Former-commit-id: 6285cc048487b05144217ded695c33781b86caa6 [formerly 91b701e1d90acb045f88f60f9827f5d322300694]
Former-commit-id: 8cb252c59f8361a1a601c073c340ef91c197de3b
Former-commit-id: 743fa2f94c0538d39c6d528920c78ddc634edde0
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox