added PublishWorkflowListener

see https://github.com/symfony-cmf/RoutingExtraBundle/pull/58

we can then remove the logic from the ``ContentController``:
https://github.com/symfony-cmf/ContentBundle/pull/22

i would suggest to not implement the ``PublishWorkflowInterface`` in the ``Route``, maybe not even in the ``StaticContent`` classes anymore.

/cc @elHornair @dbu