OPT: add default for path to the warped template
OPT: add default for path to the warped template

Former-commit-id: 188df6f192d6ad6be26a7f81898b486fb7ccba26
Former-commit-id: 90ac7b2f6c2658a62ac9b0951ed8bf353960cd09
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox