Fixed queryset so that EventDetailView will work too.

src/events/mixins.py

@@ -48,6 +48,8 @@ class EventDetailMixin(object):
 
         :return: a django QuerySets
         """
+        if self.model == models.Event:
+            return models.Event.objects.all()
         try:
             self.event = models.Event.objects.get(pk=self.kwargs['event'])
             queryset = self.model.objects.filter(event=self.event)