Added extensions function!
Example:

1. create a folder in /admin/extensions (e.g. "test")
2. create a php file in there /admin/extensions/<folder>/file.php (e.g.
"start.php"
3. create a file in the root of /admin/extensions with the format:
extmenu_<name>.php (e.g. "extmenu_test.php")
4. write a link in there (e.g. "<a
href="?page=test/start.php">Start</a>")
5. thats it!

The system will automatically integrate the extmenu_*.php menu file and
look up the extensions folder.