[Bug 999589] Synonyms in localized search.

Some of the commits that got squashed into this had these commit messages:

* Models and migrations.
* Basic admin and read-only bulk.
* Hawt bulk editor.
* Reduce duplication
* They work! Only at index creation though.
* Implement commit-to ES
* Update help.
* Feedback
* Remove debugging code.
* Fix problems with filter order.
* Don't cache synonyms on the admin page.
* Add tests for synonym searches.
* Enable localized search for questions.
* Feedback Round 2