Revert "REF: Make 'step' mandatory. See issue #1034"
Revert "REF: Make 'step' mandatory. See issue #1034"

This reverts commit e2de43324daf8c216da82bc3df70c7cf4e592066.

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