Keyword/phrase filtering (#7905)

* Add keyword filtering

    GET|POST       /api/v1/filters
    GET|PUT|DELETE /api/v1/filters/:id

- Irreversible filters can drop toots from home or notifications
- Other filters can hide toots through the client app
- Filters use a phrase valid in particular contexts, expiration

* Make sure expired filters don't get applied client-side

* Add missing API methods

* Remove "regex filter" from column settings

* Add tests

* Add test for FeedManager

* Add CustomFilter test

* Add UI for managing filters

* Add streaming API event to allow syncing filters

* Fix tests

config/navigation.rb

@@ -16,6 +16,7 @@ SimpleNavigation::Configuration.run do |navigation|
       settings.item :follower_domains, safe_join([fa_icon('users fw'), t('settings.followers')]), settings_follower_domains_url
     end
 
+    primary.item :filters, safe_join([fa_icon('filter fw'), t('filters.index.title')]), filters_path, highlights_on: %r{/filters}
     primary.item :invites, safe_join([fa_icon('user-plus fw'), t('invites.title')]), invites_path, if: proc { Setting.min_invite_role == 'user' }
 
     primary.item :development, safe_join([fa_icon('code fw'), t('settings.development')]), settings_applications_url do |development|