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/pages/demo/blank.njk

@@ -1,15 +0,0 @@
-<!-- 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 %}