add flags to permissions groups

Flags can be added to permissions group to store some metadata.

An interface `PermissionsGroupFlagProvider` allow to add some flag to the form which create/
edit permissions groups.

Entity/PermissionsGroup.php

@@ -43,6 +43,12 @@ class PermissionsGroup
      */
     private $name;
     
+    /**
+     *
+     * @var string[]
+     */
+    private $flags = [];
+    
     /**
      *
      * @var \Doctrine\Common\Collections\Collection
@@ -109,6 +115,19 @@ class PermissionsGroup
         }
     }
     
+    public function getFlags()
+    {
+        return $this->flags;
+    }
+
+    public function setFlags(array $flags)
+    {
+        $this->flags = $flags;
+        
+        return $this;
+    }
+
+        
     /**
      * Test that a role scope is associated only once with the permission group
      *