Add not-found route

app/router.js

@@ -52,6 +52,8 @@ Router.map(function () {
     this.route('payment-sent');
   });
 
+  this.route('not-found', { path: '/*path' });
+
   this.route('releases', function () {
     this.route('beta');
     this.route('canary');

app/routes/not-found.js

@@ -0,0 +1,14 @@
+import Route from '@ember/routing/route';
+import { inject as service } from '@ember/service';
+
+export default class NotFoundRoute extends Route {
+  @service fastboot;
+
+  beforeModel() {
+    if (!this.fastboot.isFastBoot) {
+      return;
+    }
+
+    this.fastboot.response.statusCode = 404;
+  }
+}

app/templates/not-found.hbs

@@ -0,0 +1,6 @@
+{{page-title "Page Not Found"}}
+
+<div class="container">
+  <h1>Page Not Found</h1>
+  <p>We couldn't find what you were looking for.</p>
+</div>