OPT: added useful module "is3d"
OPT: added useful module "is3d"

Former-commit-id: f0840dbe98fa06d0390f14b8c00f718f2a1dea6d
Former-commit-id: c7505af50a7679874c98a4ec8cd58848fb6cbd7c
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox