NEW: added new biplane smoothing in msct_smooth using ITK
NEW: added new biplane smoothing in msct_smooth using ITK

Former-commit-id: b7ec23900e7ea56cf70c95ce12d50daa17e0f4d0
Former-commit-id: fc36dd9e9e2a1fbf28dfa92f1efaa43e14fb87d5
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox