Shared settings

This is a follow up of gh-2365.
This should fix the remaining issue in web.

To test:
- Login as user-4, import two images.
- Go and change the rendering settings to Red.
- Login to Web as user-6 = admin and view the same image.
- Still as admin in web, change the Rnd to Pink and Save (not Apply & Save, just Save).
- Check that The Full Viewer updates, the Preview updates as well to Pink, and  Thumb does
- Still in Web as admin, hit Reset -> image goes grey as expected
- Go to Insight as user-4 and view the image. User-4 can see his own settings (Red)
- But under Saved by, the user-6's (=admins) settings should be grey
 - Still as user-4 in Insight, choose user-6's settings and Save
 - the image goes grey, the thumbnail of the user-6 is now grey