Changed cookie access to use CodeIgniter input class instead of direct access

CodeIgniter has built in methods for accessing cookies. The benefit of using these is that it protects you from XSS attacks.

$_POST, $_GET, $_SESSION and $_COOKIE shouldn't be accessed directly if you're using CodeIgniter. The input class should be used.

http://ellislab.com/codeigniter/user-guide/libraries/input.html