#1723

@rande #1723 added prototype for code like
```
$formMapper
    ->with('tab1', array('tab'=>true))
        ->with('group1')
            ->add('username')
            ->add('password')
        ->end()
        ->with('group2', array('collapsed' => true))
            ->add('enabled')
            ->add('createdAt')
        ->end()
    ->end();
```
``tab`` should be false per default