improve classes

Example of usage:

    /**
     * @Route("/")
     * @Template()
     */
    public function indexAction()
    {
        $qb = $this->getDoctrine()->getManager()->getRepository('TestBundle:Estado')->createQueryBuilder('e');

        $grid = $this->get('tao_sistemas_ajax_grid.manager')->newGrid($qb);

        $grid->addColumn('Id', 'e.id')
             ->addColumn('Name', 'e.name')
             ->addColumn('Description')
        ;

        $grid->setSortedColumn(1);
        $grid->setSortedDirection('desc');

        $grid->generateView();

        return array('grid' => $grid);
    }