Added templates for http exceptions.

dav_events/templates/404.html

@@ -0,0 +1,6 @@
+{% extends "error_base.html" %}
+
+{% block error-code %}404{% endblock %}
+{% block error-title %}Not Found{% endblock %}
+{% block error-heading %}Ressource nicht gefunden{% endblock %}
+{% block error-body %}<p>{{ exception }}</p>{% endblock %}