notification: add more variable in twig template

src/Bundle/ChillActivityBundle/Resources/views/Activity/showInNotification.html.twig

@@ -1,2 +1,10 @@
-
-<a href="{{ path('chill_activity_activity_show', {'id': notification.relatedEntityId })  }}">Go to Activity</a>
+{# available variables: notification, activity #}
+{% if activity is not null %}
+    {% if is_granted('CHILL_ACTIVITY_SEE', activity) %}
+        <a href="{{ path('chill_activity_activity_show', {'id': activity.id })  }}">Go to Activity</a>
+    {% else %}
+        you are not allowed to see it details. This is the minimal data: {{ activity.id }}
+    {% endif %}
+{% else %}
+    You get notified of an activity which does not exists any more.
+{% endif %}