Added removeBeforeFilter and removeAfterFilter controller methods.

This adds the ability to remove before and after controller filters if they are identifiable by a string. This is useful if you have a base controller that adds a before or after filter, but some of its children shouldn't use that filter.

I'm open to any suggestions about how to improve this or any added functionality. I added it to 4.1 because it should be completely non-breaking since it uses all new functions. I also ran the tests in RoutingRouteTest.php which is where I added my new tests, and it was green.

Say you had a BaseController that all controllers extended, and also a ConfigurationsController. You want CSRF protection on all posts, except for those in ConfigurationsController. You can just do something like this:

```
class BaseController extends Controller {
    public function __construct()
    {
        $this->beforeFilter('csrf', array('on' => ['post', 'put', 'patch', 'delete']));
    }
}

class ConfigurationsController extends Controller {
    function __construct()
    {
        parent::__construct();
        $this->removeBeforeFilter('csrf');
    }
}
```