Ajout d'un bouton annuler quand on modifie un événement

Fix #62

src/agenda_culturel/templates/agenda_culturel/event_form.html

@@ -22,7 +22,10 @@
 
 <form method="post">{% csrf_token %}
     {{ form.as_p }}
-    <input type="submit" value="Enregistrer">
+    <div class="grid">
+        <a href="{% if request.META.HTTP_REFERER %}{{ request.META.HTTP_REFERER }}{% else %}{{ object.get_absolute_url }}{% endif %}" role="button" class="secondary">Annuler</a>
+        <input type="submit" value="Enregistrer">
+    </div>
 </form>
 
 {% endblock %}