improve demo app

examples/demo/main.js

@@ -1,10 +1,13 @@
 import { App } from "./app.js";
-import { Counter } from "./counter.js";
 
-document.addEventListener("DOMContentLoaded", function() {
+function createApp(el) {
   const env = {
     qweb: new odoo.core.QWeb()
   };
   const app = new App(env, { initialState: 13 });
-  app.mount(document.body);
+  app.mount(el);
+}
+
+document.addEventListener("DOMContentLoaded", function() {
+  createApp(document.body);
 });