Fixes on favorites plugin - multiple sets

[bic-ed]

• [x] Avoid duplicate instances of the same image Using one of the two methods proposed
• [x] Fix Users watching list in admin page The raw serialized aux field is now printed for instances: a:2:{i:0;s:7:"User";i:1;s:9:"Instance";}
• [x] Make the name of groups (instances) case-insensitive, since instance options are case-insensitive
• [x] Prevent tag_suggest bind code from output when not needed (i.e. most of the times)

[bic-ed]

Questions

• Which method is best to use to avoid duplicates?

  • The one added to addImage() does the job with just one query, but I'm not sure it's bulletproof. Tested in my local env it works properly though
  • The one added to addAlbum() uses two different queries, but it seems bulletproof to me and also skips the filter* if no new option is set

• What does this filter do? *zp_apply_filter('favoritesHandler_action', 'add', $img, $this->name);

• Remove text/javascript attribute and CDATA from tag_suggest bind javaScript?