Simple fix to make templates configurable

This simple fix makes the templates configurable like other CMF content.

```yml
symfony_cmf_routing_extra:
    dynamic:
        templates_by_class:
            Symfony\Cmf\Bundle\BlogBundle\Document\Blog: SiteBundle:Blog:list.html.twig
            Symfony\Cmf\Bundle\BlogBundle\Document\Post: SiteBundle:Blog:post.html.twig
```