Mix back some of the changes from previous check-in with additional fixes

Mix back some of the changes from previous check-in with additional fixes
and a cleaner version of the table.
* Clean up EXIF display table:
- use localized description of items
- don't forget to HTML-encode the localized messages!
- clean up the style a bit on the middle spacer
- distinguish the header and data columns a little better
* Don't show 'edit this image' link if no file exists