OPT: Include sct_register_multimodal, code more clean
OPT: Include sct_register_multimodal, code more clean

Former-commit-id: ac70174e5bfae7bbeb4b2043d3de544f1ccb7327
Former-commit-id: 61cd6e010fcdd38acc4bf66d4e4d52405664df3b
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox