ENH: now using nibabel for i/o
ENH: now using nibabel for i/o

Former-commit-id: f3e5de5f6a55c634cbb06fd8b776e27434d36687
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox