OPT: fixed straightening. now using rigid transformation. Still need to fix registration to template
OPT: fixed straightening. now using rigid transformation. Still need to fix registration to template

Former-commit-id: 1d6c42c5c32b1015227897bee3a7901c5adb48e3 [formerly e1a4a2af1713a43b1e9c6faa1c70fbd7fdbc88f2]
Former-commit-id: d6a923623ffbb868039ba75ed7433c8e64ead1d9
Former-commit-id: 4332b49da6b65b9f96f0bb51a535db2a94f900d9
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox