title: toString method for SonataAdminBundle Listing in Symfony2
body: <p>In Symfony 2.3 i am using SonataAdminBundle ( master ) and i am trying to get ManyToMany working in Listing. The Problem is that SonataAdminBundle is asking for a toString() method. Implementing this method to the related Entity solves the problem.</p>
  
  <p>My Question: Do i have to implement the toString method or is there a Option to tell SonataAdminBundle a property for using instead of calling the toString method? </p>
  
  <p>Thank you</p>