Add semantic hover states (success, info, etc.) for dropdown items

Add `.primary`, `.success`, `.info`, `.warning`, and `.danger` classes for semantic hover states on dropdown items.  Usage:

    <li class="success"><a href="#>Dropdown Item</a></li>


JS Bin: http://jsbin.com/junaripo/4/edit?html,css,output
Curly brace is on a new line here.