OPT: cross in input labels are now computed into straight space. msct_register_landmarks is back. Fixed #581
OPT: cross in input labels are now computed into straight space. msct_register_landmarks is back. Fixed #581

Former-commit-id: 1e5d320a51ce55d0498cbb60f448142c58c46b44
Former-commit-id: b1c76d270fc1cb3cb3769fb0bbf6a3a11cc5c3df
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox