REF: new version of batch processing using sct_register_graymatter
REF: new version of batch processing using sct_register_graymatter

Former-commit-id: 004fbfa1e995d729c9a8cb7eae5e44b8d18824b0
Former-commit-id: 7a71ae5c1e687eb3e6bb43c535035b4628880c2f
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox