Spw thumbs 10827 develop

This PR combines 2 PRs that are in dev_4_4:
 - getThumbnail to use cached thumbs https://github.com/openmicroscopy/openmicroscopy/pull/746
 - Fix cached thumbs bug (4.4.8 bug fix) https://github.com/openmicroscopy/openmicroscopy/pull/1127

To test, try to view SPW for another user in a Read-Only or Private group. Check that thumbnails are visible in the Wells.