feat: Change app template

- Add global variables to app template
- Add flag colors to global variables
- Change var declaration

source/templates/demo/_app.njk

@@ -23,6 +23,8 @@
     {% block body %}{% endblock %}
 
     {% block script %}
+      <script src="https://code.jquery.com/jquery-3.3.1.min.js" integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
+      <script src="{{ pageBase }}js/variables.js"></script>
     {% endblock %}
 
   </body>