make logout a POST operation

core/templates/core/base/header.jinja

@@ -59,7 +59,10 @@
             </div>
             <div class="links">
               <a href="{{ url('core:user_tools') }}">{% trans %}Tools{% endtrans %}</a>
-              <a href="{{ url('core:logout') }}">{% trans %}Logout{% endtrans %}</a>
+              <form id="logout-form" method="post" action="{{ url("core:logout") }}">
+                {% csrf_token %}
+                <button type="submit">{% trans %}Logout{% endtrans %}</button>
+              </form>
             </div>
           </div>
           <a