OPT: added param to compute model in command line with msct_multiatlas_seg
OPT: added param to compute model in command line with msct_multiatlas_seg

Former-commit-id: e62be3e1c6f08a403e3b891b79d431281fbfe5e6 [formerly 9c8a17e002a33b091188f2f782819811cd1ab3a0]
Former-commit-id: 63091d13eb8fe1df915078b1d9bbc752cb59f13c
Former-commit-id: 3ce8eefdecbb5947bcb9588bb4ce46c3e67478a7
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox