REF: now possible to input gradientStep
REF: now possible to input gradientStep

Former-commit-id: 2f07b45455e5dba2dbfac59a36a2bf26372f3b05
Former-commit-id: 1f1cab680276bed4b9b1f7ac4efda305b059651a
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox