DEV: Creation of a class ExtractCenterline to be used for the process of the extraction of the centerline. This done by assuming that nurbs smoothing method will work with the concatenation of segmentation and label parts
DEV: Creation of a class ExtractCenterline to be used for the process of the extraction of the centerline. This done by assuming that nurbs smoothing method will work with the concatenation of segmentation and label parts

Former-commit-id: d6f5be027c659e8aecd105d9cb4065f0a82ff23c [formerly 6fd8512736016e1d64ec656b3f8028c57113e238]
Former-commit-id: 961b4e9e5b6d3fb5f6524db73984bb9c3cfb4d3e
Former-commit-id: ac2f1abdc737fe54c139fcd7a7e251b1e6dbf161
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox