Call setter on filter obj if set$optionkey exists

This allows you to do things like set the Scss/Sass filter style for
minification.

```php
<?php
return array(
    ...
    'filters' => array(
        'SassFilter' => array(
            'name' => 'Assetic\Filter\Sass\SassFilter',
            'style' => 'compressed', /* call
$filter->setStyle('compressed'); */
        ),
    ),
);
```