OPT: register_multimodal: added warning to ignore masking for centermass
OPT: register_multimodal: added warning to ignore masking for centermass

Former-commit-id: 4d38d325cd86488bea4313c3cdfc4de57c940121 [formerly df18469e47d0845e666bfc9859d8f89ad85df945]
Former-commit-id: 1d0fac855f8d4ceecd1195492178cdd9e244b678
Former-commit-id: d42513bc68cdb9b8c5efc881b4f481633d9c043f
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox