Improve the public hashtag page (#9831)

- Fix height not updating when clicking show more on public hashtag page
- Add header to the public hashtag page
- Change text size and margins on the public hashtag page

app/javascript/mastodon/features/standalone/hashtag_timeline/index.js

@@ -80,7 +80,7 @@ class HashtagTimeline extends React.PureComponent {
           <div className='statuses-grid__item' key={statusId}>
             <DetailedStatusContainer
               id={statusId}
-              showThread
+              compact
               measureHeight
               onHeightChange={this.handleHeightChange}
             />