Add generic error catchers

templates/errors/404.html.tera

@@ -0,0 +1,6 @@
+{% extends "errors/base" %}
+
+{% block error %}
+    <h1>{{ "We couldn't find this page." | _ }}</h1>
+    <h2>{{ "The link that led you here may be broken." | _ }}</h2>
+{% endblock error %}