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/index.js

@@ -101,7 +101,7 @@ export default class Compose extends React.PureComponent {
         {(multiColumn || isSearchPage) && <SearchContainer /> }
 
         <div className='drawer__pager'>
-          <div className='drawer__inner' onFocus={this.onFocus}>
+          {!isSearchPage && <div className='drawer__inner' onFocus={this.onFocus}>
             <NavigationContainer onClose={this.onBlur} />
             <ComposeFormContainer />
             {multiColumn && (
@@ -109,7 +109,7 @@ export default class Compose extends React.PureComponent {
                 <img alt='' draggable='false' src={elephantUIPlane} />
               </div>
             )}
-          </div>
+          </div>}
 
           <Motion defaultStyle={{ x: isSearchPage ? 0 : -100 }} style={{ x: spring(showSearch || isSearchPage ? 0 : -100, { stiffness: 210, damping: 20 }) }}>
             {({ x }) => (