Equalise spacing

Make the amount of space above and below is equal, and consistent with
the spacing when we show the checkbox.

app/templates/views/service-settings/email-reply-to/edit.html

@@ -19,7 +19,7 @@
       safe_error_message=True
     ) }}
     {% if form.is_default.data %}
-      <p>
+      <p class="form-group">
         This email address is the default
       </p>
     {% else %}