gulp tasks and nunjucks templating

- reworked nearly all gulp tasks
- added html templating with nunjucks
- replaced some old html files
- started correction of scss and js files according to lint results

source/code/variables.js

@@ -1,3 +1,5 @@
+'use strict';
+
 var w = Math.max(document.documentElement.clientWidth, window.innerWidth || 0);
 var h = Math.max(document.documentElement.clientHeight, window.innerHeight || 0);