Returned value of "move" method should be compatible with Cmf PhpcrTree

The PhpcrOdmTree "move" method returns only the id of the moved document.
https://github.com/sonata-project/SonataDoctrinePhpcrAdminBundle/blob/master/Tree/PhpcrOdmTree.php#L157

The Cmf PHPCRTree one returns an hash { id: value, safe_url_id: value }
https://github.com/symfony-cmf/TreeBrowserBundle/blob/master/Tree/PHPCRTree.php#L66

This PR fixes the wrong behavior in the javascript rendered tree when you move a document in a different tree position.
https://github.com/symfony-cmf/TreeBrowserBundle/blob/master/Resources/public/js/admin_tree.js#L229