Fix various things in the directory (#9449)

* Fix missing variable in directory page title

* Order hashtags by number of people instead of alphabetically

* Add icon to OpenGraph preview of directory page

* Prevent line breaks in hashtags and ensure lowercase in the table

app/javascript/styles/mastodon/widgets.scss

@@ -300,6 +300,9 @@
       font-size: 18px;
       font-weight: 700;
       color: $primary-text-color;
+      white-space: nowrap;
+      overflow: hidden;
+      text-overflow: ellipsis;
 
       .fa {
         color: $darker-text-color;