add custom 404 for GA

Author: kmurphypolygon

overrides/404.html

@@ -0,0 +1,9 @@
+{% extends "main.html" %}
+
+{% block content %}
+  <h1>404 - Not found</h1>
+{% endblock %}
+
+{% block htmltitle %}
+   <title>404 - Not found</title>
+{% endblock %}