OPT: register_to_template: added flags to set straightening: param-straighten
OPT: register_to_template: added flags to set straightening: param-straighten

Former-commit-id: c262c53c8aee1e0735da99a11f3f79cb4e21ca6f
Former-commit-id: 7c0038a4c3b07debe8c02d6eadb4c681bd043ae5
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox