preliminary commit to save the first part of the implementation for issue #736 (distinction between individual and combined tracts)
preliminary commit to save the first part of the implementation for issue #736 (distinction between individual and combined tracts)

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox