Delay reindexing apps in collections, don't use ES any more in preview mode (bug 950839, bug 950238)

https://bugzilla.mozilla.org/show_bug.cgi?id=950839
https://bugzilla.mozilla.org/show_bug.cgi?id=950238

These 2 go together: it's a good thing to delay reindexing apps when dealing with collections, but this means we need to stop using ES when we are in preview mode in the curation tool.