chore(client): Move client app to /client

client/src/pages/404.js

@@ -0,0 +1,11 @@
+import React from 'react';
+import Layout from '../components/Layout';
+
+const NotFoundPage = () => (
+  <Layout>
+    <h1>NOT FOUND</h1>
+    <p>You just hit a route that doesn&#39;t exist... the sadness.</p>
+  </Layout>
+);
+
+export default NotFoundPage;