* 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

- Restrict followers counts to local users to minimize local advantage
- Fix emoji shortcodes causing error in search
- Fix search syntax parse errors not being caught

* Add more accurate account search

When ElasticSearch is available, a more accurate search is implemented:

- Using edge n-gram index for acct and display name
- Using asciifolding and cjk width normalization on display names
- Using Gaussian decay on account activity for additional scoring (recency)
- Using followers/friends ratio for additional scoring (spamminess)
- Using followers number for additional scoring (size)

The exact match precedence only takes effect when the input conforms
to the username format and the username part of it is complete, i.e.
when the user started typing the domain part.

* Support single-letter usernames

* Fix tests

* Fix not picking up account updates

* Add weights and normalization for scores, skip zero terms queries

* Use local counts for accounts index, adjust search parameters

* Fix mistakes

* Using updated_at of accounts is inadequate for remote accounts

* Apply filters to poll options in WebUI

Fixes #11128

* Apply filters to poll options server-side

* Add poll options to searchable text

* Add type, limit, offset, min_id, max_id, account_id to search API

Fix #8939

* Make the offset work on accounts and hashtags search as well

* Assure brakeman we are not doing mass assignment here

* Do not allow paginating unless a type is chosen

* Fix search query and index id field on statuses instead of created_at

* Add image descriptions to searchable post content.

* Allow multi-line image descriptions.

* Request image descriptions in the same query as posts when creating the search index.

(see https://github.com/tootsuite/mastodon/pull/10036#discussion_r256551624)

* Add full-text search for authorized statuses

- Search API will return statuses that match the query
- Only for logged in users
- Only if you are author of the status,
- Or you were mentioned in it
- Or you favourited or reblogged it
- Configuration over `ES_ENABLED`, `ES_HOST`, `ES_PORT`, `ES_PREFIX`
- Run `rails chewy:deploy` to create & populate index

Fix #5880
Fix #4293
Fix #1152

* Add commented out docker-compose configuration for ES container

* Optimize index import, filter search results

* Add basic normalization to the index

* Add better stemming and normalization to the index

* Skip webfinger request if search query includes both @ and a space

* Fix code style

* Visually separate search result sections

* Fix code style issues