FIX: Bookmark search fixes (#10239)

* Remove unneeded bookmark name index.
* Change bookmark search query to use post_search_data. This allows searching on topic title and post content
* Tweak the style/layout of the bookmark list so the search looks better and the whole page fits better on mobile.

db/migrate/20200715030908_remove_unneccessary_bookmark_name_index.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class RemoveUnneccessaryBookmarkNameIndex < ActiveRecord::Migration[6.0]
+  def change
+    remove_index :bookmarks, :name
+  end
+end