OPT: shortened code; now call functions from msct_register
OPT: shortened code; now call functions from msct_register

Former-commit-id: 9d7ba3341483d00d2d1f5a2473e6e060ebc54c31
Former-commit-id: 407c129c8b4065c4b37729e538d1e0f4d4fe531a
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox