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/common.js

@@ -4,5 +4,9 @@ export function start() {
   require('font-awesome/css/font-awesome.css');
   require.context('../images/', true);
 
-  Rails.start();
+  try {
+    Rails.start();
+  } catch (e) {
+    // If called twice
+  }
 };