Allow to use disabled class in dropdowns

Created by: Serhii-DV

I would like to use it something like that:

<ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu">
  <li><a tabindex="-1" href="#">Action</a></li>
  <li><a tabindex="-1" href="#" class="disabled">Disabled action</a></li>
  <li><a tabindex="-1" href="#">Something else here</a></li>
  <li class="divider"></li>
  <li><a tabindex="-1" href="#">Separated link</a></li>
</ul>