add nurbs_pts_number as parameter of sct_process_segmentation.smooth_centerline
add nurbs_pts_number as parameter of sct_process_segmentation.smooth_centerline


Former-commit-id: a5d84398ee25df989d517f0ddfdf36103e4ccbb3
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox