Update controller.php

 * - Constructor adds a 'config' attribute to the Controller object, so one can use $this->config within controller methods, rather than "global $config" in every single function
 * - changed loadHelper() so helper PHP files are named simply Thing.php instead of Thing_helper.php  Not a big change, but nicer filenames
 *   other conventions left unchanged, e.g. class name is still Session_helper and $session = $this->loadHelper('Session') returns a Session_helper instance