Fix #21

1. GlsrGestockBundle:Supplier::deleteAction
   * test if supplier has articles
   * give the list of these article to ArticleController
2. GlsrGestockBundle:Article::reassignAction
   * create form with a select for the possible supplier to reassign articles
   * This form is create manualy. #22 Find another way to present the matter
Merge pull request #23 from GLSR/developp

Fix #21