Major step for build process

- updated to 0.4.0
- corrected license for npm
- update to gulp 4
- updated all dependencies
- new and removed packages, see `package.json`
- changed file structure, renamed `pages` to `screen` and new `data` 
folder
- complete change of `gulpfile.js` with similar output

source/screens/demo/maintenance.njk

@@ -0,0 +1,17 @@
+<!-- page-maintenance.njk -->
+{% set pageId = "blank" %}
+{% set pageClass = "height_full" %}
+
+{% extends "demo/maintenance.njk" %}
+
+{% block title %}Maintenance{% endblock %}
+
+{% block head %}
+{{ super() }}
+{% endblock %}
+
+{% block body_content %}
+<div id="root" class="overflow">
+	<h1 class="txt_hero txt_center txt_gradient">HIPPIE</h1>
+</div>
+{% endblock %}