feat!: move every layout to demo folder

- source/screens is now free for user files
- rename demo templates to their equivalent sources
- add demo maintenance template
- demo templates use html base element

source/templates/demo/_main.njk

@@ -0,0 +1,23 @@
+<!-- demo.main.template -->
+{% extends "hippie/_main.njk" %}
+
+{% block meta %}
+  {% include "demo/partials/_meta.njk" %}
+  <base href="/">
+{% endblock %}
+
+{% block links %}
+  {{ super() }}
+  <!--[if lte IE 9]> <script src="https://cdn.jsdelivr.net/html5shiv/3.7.3/html5shiv.min.js"></script> <![endif]-->
+  <!--[if lte IE 9]> <script src="https://cdn.jsdelivr.net/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script> <![endif]-->
+  <!--Local alternative: <script src="./code/html5shiv.min.js"></script>-->
+  <!--Only use one of the above!-->
+
+  <!-- <link href='https://fonts.googleapis.com/css?family=Roboto:400,300,400italic,500,500italic,700' rel='stylesheet' type='text/css'> -->
+  <!-- <link rel="stylesheet" type="text/css" media="print" href="{{ pageBase }}css/print.css"/> -->
+{% endblock %}
+
+{% block script %}
+  {{ super() }}
+  <script src="https://code.jquery.com/jquery-3.3.1.min.js" integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
+{% endblock %}