Add missing template

app/templates/error.html

@@ -0,0 +1,12 @@
+{%- import "utils.html" as utils with context -%}
+{% extends "layout.html" %}
+
+{% block head %}
+<title>{{ title }}</title>
+{% endblock %}
+
+{% block content %}
+<div class="centered primary-color">
+    <h1>{{ title }}</h1>
+</div>
+{% endblock %}