add app config and settings generator

templates/error.html

@@ -0,0 +1,17 @@
+{% extends 'base.html' %}
+
+{% block title %}Error{% endblock %}
+
+{% block content %}
+<div class="container py-5">
+  <div class="alert alert-danger" role="alert">
+    <h4 class="alert-heading">An error occurred</h4>
+    <p>{{ message|safe }}</p>
+    {% if error and error.code %}
+      <hr>
+      <p class="mb-0">Error code: {{ error.code }}</p>
+    {% endif %}
+    <a href="{{ url_for('index') }}" class="btn btn-secondary mt-3">Back to Home</a>
+  </div>
+</div>
+{% endblock %}