REF: propseg: changed variable names according to convention
REF: propseg: changed variable names according to convention

Former-commit-id: 6bf8d262a01f3c7e571b2c48dd858a64900cb66d
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox