added validations groups Registration

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: -
Todo: -

Admin/Entity/GroupAdmin.php

@@ -19,6 +19,10 @@ use Sonata\AdminBundle\Route\RouteCollection;
 
 class GroupAdmin extends Admin
 {
+    protected $formOptions = array(
+        'validation_groups' => 'Registration'
+    );
+
     public function getNewInstance()
     {
         $class = $this->getClass();
@@ -47,4 +51,4 @@ class GroupAdmin extends Admin
             ->add('roles', 'sonata_security_roles', array( 'multiple' => true, 'required' => false))
         ;
     }
-}
+}