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/screens/pages/maintenance.njk

@@ -1,18 +0,0 @@
-<!-- maintenance.page -->
-{% set pageBase = "../" %}
-{% set pageId = "blank" %}
-{% set pageClass = "h_full_view" %}
-
-{% extends "hippie/_maintenance.njk" %}
-
-{% block title %}Maintenance{% endblock %}
-
-{% block head %}
-{{ super() }}
-{% endblock %}
-
-{% block main %}
-<div id="root" class="overflow">
-  <h1 class="txt_hero txt_center txt_gradient">HIPPIE</h1>
-</div>
-{% endblock %}