Configure tagName to label

Hi,

As you can see in https://github.com/twbs/bootstrap/blob/master/dist/css/bootstrap.css#L4135
It's possible to use label with href attribute, so I added possiblity to change default tagName, you should use like that:
```php
$this->label('Removed', array('tagName' => 'a', 'href' => '/home/removed'));
```