Always show order poll questions by created at

PostgreSQL doesn't guarantee the order of the records, so we have to
specify it if we want the questions to be displayed in a consistent
order.

app/views/admin/poll/polls/_questions.html.erb

@@ -15,7 +15,7 @@
         <th><%= t("admin.actions.actions") %></th>
       </tr>
     </thead>
-    <% @poll.questions.each do |question| %>
+    <% @poll.questions.sort_for_list.each do |question| %>
       <tr id="<%= dom_id(question) %>">
         <td>
           <strong><%= question.title %></strong>