sct_deepseg_gm: use CLAHE by default for QC
sct_deepseg_gm: use CLAHE by default for QC


Former-commit-id: 51dbcf2fcfa485c0034af7c9c710d19711c50566
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox