OPT: detect_vertebral_levels: now fully working for T1
OPT: detect_vertebral_levels: now fully working for T1

Former-commit-id: 0c57393049a128896afbc31969e9134e3328722f [formerly f294af4474762cdba04628949c2a5a65f241e9b7]
Former-commit-id: 6ccb9d66d4be1c10732ae67799d2ecf3c433a85b
Former-commit-id: 4f33c15d2456f8c6d8f2c5432a1ff4988e504934
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox