OPT: now separating first and second registration algorithms in sct_register_multimodal
OPT: now separating first and second registration algorithms in sct_register_multimodal

Former-commit-id: abf252076adb479bb5da64e864b66ee986c3d917 [formerly 8c4f2f6fa18853bde443b850b99fc8cb62ec592f]
Former-commit-id: b6519a316fc6e92617dfcdd23bda9165e4fc24b4
Former-commit-id: d5c43b0218a5299e331608887fecf707aba929d4
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox