Support for jquery ui 1.11

jQuery UI 1.11 [removed the requirement](http://jqueryui.com/upgrade-guide/1.11/#menu) to use anchors in menu items. Markup containing anchors will still work, but there are styling issues. This PR adds support for initialization of the menu from an anchor-less HTML markup.

A breaking change is that the menu command was moved from the `<a>` element's `href` attribute to the `data-command` attribute of the `<li>` element.