Ability to use form-control-static

https://github.com/phiamo/MopaBootstrapBundle/issues/782

Example usage:

Note: Automatically disables field.

```
        $builder->add('username', 'text', array(
            'static_text' => true,
            'horizontal_label_class' => 'col-md-3',
            'horizontal_input_wrapper_class' => 'col-md-4'
        ));
```