Suggestion: creating a cookie object for both the request and response

On top of the ability to create cookies with the `AbstractResponse::cookie()` method, it would be nice to be able to create `Cookie` objects and add them like so:

```php
$myCookie = new Cookie();
$myCookie->setName('my_cookie');
$myCookie->setValue('my_value');

$response->addCookie($cookie);
```

This is just to open the discussion, as the commits don't do much yet.