NEW: normalization using median values instead of mean values in the WM and GM (more robust)
NEW: normalization using median values instead of mean values in the WM and GM (more robust)

Former-commit-id: e9166ecab92af642591a85143bb15f727d3976d4
Former-commit-id: e447bbf483e9cb84cebada472da82b99859cfc0e
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox