Factor out the update button into its own small template

For code reuse, you know

templates/accounts.html

@@ -11,10 +11,7 @@
     <td>{{ account.source.name }}</td>
     <td>{{ account.last_updated }}</td>
     <td>
-      <form method="POST" action="/update/">
-        <input type="hidden" name="account_uuid" value="{{ account.uuid }}"></input>
-        <input type="submit" value="Update" class="btn btn-primary"></input>
-      </form>
+      {% include 'update_button.html' %}
     </td>
   </tr>
   {% endfor %}