Track trending tags (#7638)

* Track trending tags

- Half-life of 1 day
- Historical usage in daily buckets (last 7 days stored)
- GET /api/v1/trends

Fix #271

* Add trends to web UI

* Don't render compose form on search route, adjust search results header

* Disqualify tag from trends if it's in disallowed hashtags setting

* Count distinct accounts using tag, ignore silenced accounts

app/javascript/mastodon/features/compose/containers/search_results_container.js

@@ -1,8 +1,14 @@
 import { connect } from 'react-redux';
 import SearchResults from '../components/search_results';
+import { fetchTrends } from '../../../actions/trends';
 
 const mapStateToProps = state => ({
   results: state.getIn(['search', 'results']),
+  trends: state.get('trends'),
 });
 
-export default connect(mapStateToProps)(SearchResults);
+const mapDispatchToProps = dispatch => ({
+  fetchTrends: () => dispatch(fetchTrends()),
+});
+
+export default connect(mapStateToProps, mapDispatchToProps)(SearchResults);