OPT: now estimating center of mass of the centerline/segmentation to address issue #33.
OPT: now estimating center of mass of the centerline/segmentation to address issue #33.

Former-commit-id: b1d0cfe977fbd660fc37e9341a98fe738009975a
Former-commit-id: b4e8b04e82262ab2cddbf434ddb3a1fe0e9c612c
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox