Extensions pages

Add or update the following Extensions page: Home, Extensions Team Overview, phpBB Official Extensions, Extensions Development Team Overview, Installing, Extensions Rules and Guidelines, Recognised Extension Developers.
Should be
``` php
/**
 *
 * @package PhpbbWebsiteInterfaceBundle
 * @copyright (c) 2014 phpBB Group
 * @license http://opensource.org/licenses/gpl-3.0.php GNU General Public License v3
 * @author battye
 *
 */
```

I'll fix all the headers to the new type soonish.