INST: replaced requirements.txt with requirements.py. Fixed #644
INST: replaced requirements.txt with requirements.py. Fixed #644

Former-commit-id: b8f3518e78f7d90805b230b1407f8b2cc12f8048
Former-commit-id: a5e860d92fa3da57af9b50fac50c8d3a54eb359e
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox