Make DropDown support divider class.

[callmez]

Dropdown::widget(array(
    'items' => array(
        array('label' => 'li1', 'url' => $this->context->createUrl('site/index')),
        array('label' => '', 'options' => array('class' => 'divider')),
        array('label' => 'li3', 'url' => $this->context->createUrl('site/index')),
    )
)

[coveralls]

Coverage remained the same when pulling 0c7545c on callmez:master into b6e3dd2 on yiisoft:master.

[qiangxue]

You can directly enter "<li class="divider"></li>" as an element of items.

[callmez]

Oh, I see it. thanks