added batch action label to batch action confirmation form
integrated action_label as placeholder, adapted fr, en and de strings
force translation of action_label
Merge branch 'batch_action_label' of https://github.com/benoitpointet/SonataAdminBundle into benoitpointet-batch_action_label

Conflicts:
	Controller/CRUDController.php
	Resources/views/CRUD/batch_confirmation.html.twig