feat: Refactor project structure and add new files

- Removed old style.css and added boilerplate.css for better cross-browser compatibility.
- Introduced browserconfig.xml for Microsoft tile support.
- Created impressum.php and index.php for main application pages.
- Added info.php for PHP info display.
- Implemented mett.js and mett.min.js for Mett calculation functionality.
- Included respond.min.js for media query support in older browsers.
- Recreated style.css with responsive design features.
- Added index.html as a landing page with a placeholder message.

dev/info.php

@@ -0,0 +1,3 @@
+<?php
+phpinfo();
+?>