sct_image/concat: Introduced possibility to squeeze data
sct_image/concat: Introduced possibility to squeeze data

This is sometimes useful in case singletons need to be removed


Former-commit-id: 44076daee1e367e21ff25affbea74d550c1a01de
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox