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/data/demo.json

@@ -0,0 +1,54 @@
+{
+  "demoadditionallinks": [
+    {
+      "href": "demo/intro.html",
+      "text": "Intro"
+    },
+    {
+      "href": "demo/elements.html",
+      "text": "Elements"
+    },
+    {
+      "href": "demo/examples.html",
+      "text": "Examples"
+    },
+    {
+      "href": "demo/tests.html",
+      "text": "Tests"
+    }
+  ],
+  "demolinks": [
+    {
+      "href": "demo/blank.html",
+      "text": "Blank"
+    },
+    {
+      "href": "demo/maintenance.html",
+      "text": "Maintenance"
+    },
+    {
+      "href": "demo/error/304.html",
+      "text": "304"
+    },
+    {
+      "href": "demo/error/404.html",
+      "text": "404"
+    },
+    {
+      "href": "demo/error/403.html",
+      "text": "403"
+    },
+    {
+      "href": "demo/error/400.html",
+      "text": "400"
+    },
+    {
+      "href": "demo/error/500.html",
+      "text": "500"
+    },
+    {
+      "href": "demo/os.html",
+      "text": "OS"
+    }
+  ]
+}