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/blank.njk

@@ -0,0 +1,15 @@
+<!-- page-blank.njk -->
+{% set pageId = "blank" %}
+{% set pageClass = "height_full" %}
+
+{% extends "demo/default.njk" %}
+
+{% block title %}Blank{% endblock %}
+
+{% block head %}
+{{ super() }}
+{% endblock %}
+
+{% block body_content %}
+
+{% endblock %}