NEW: msct_gmseg_utils: LOOCV by slice including levels
NEW: msct_gmseg_utils: LOOCV by slice including levels

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox