DEV: new method to get interpolated coordinate along centerline
DEV: new method to get interpolated coordinate along centerline

Former-commit-id: 838e04532a622a6d1715d0d75b14d964f6d955bb
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox