Make it so normal search returns even unreviewed matches, but
autosuggestions do not.

Fix #11960

* Fallback to Database search when ES not available

* Prevent double work if ES gives 0 result

* Apply suggestion from code review

* Add more accurate hashtag search

Using ElasticSearch to index hashtags with edge n-grams and score
them by usage within the last 7 days since last activity. Only
hashtags that have been reviewed and are listable can appear in
searches, unless they match the query exactly

* Fix search analyzer dropping non-ascii characters