Slim instance as parameter in controller constructor

This PR addresses issue #748 by passing the \Slim\Slim application object to the controller constructor.

Just add something like the following to your controller class and \Slim\Slim object will be available within your controllers.

```php
/**
 * Constructor
 * @param \Slim\Slim $application The Slim application
 */
public function __construct(\Slim\Slim $application)
{
    $this->app = $application;
}
````