* 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
* Change hashtag search to only return results that have trended in the past
A way to eliminate typos and other one-off "junk" results
* Fix excluding exact matches that don't have a score
* Fix tests
* Sort results by the name
* Switch search method to simple `LIKE` matching instead of tsvector/tsquery
Previously we used scores from ts_rank_cd() to sort results, but it didn't work
because the function returns same score for all results. It's not for calculate
similarity of single words. Sometimes this bug even push out exact matching tag
from results.
Additionally, PostgreSQL supports prefix searching with standard btree index.
Using it offers simpler code, but also less index size and some speed.
* Clean up SQL output in Tag and Account search methods
* Add basic coverage for Tag.search_for
* Add coverage for Account.search_for
* Add coverage for Account.advanced_search_for
