Fix: mark checked button in button group as active, consistent to official bootstrap example.
Fix: mark checked button in button group as active, consistent to official bootstrap example.

Example code:

```
    $buttons = array();
    $buttons[] = array('label' => 'Foo', 'checked' => true);
    $buttons[] = array('label' => 'Bar');
    echo TbHtml::buttonGroup($buttons, array('toggle' => TbHtml::BUTTON_TOGGLE_RADIO));
```

marcovtwout/yiistrap,crisu83/yiistrap,crisu83/yiistrap,marcovtwout/yiistrap