Menu: open className and aria-expanded on li, initially set aria-expanded="false"

- Set open class on containing list item, this allows for greater flexibility in styling
- Set aria-expanded on the list item who owns the expanded menu
- Initially set aria-expanded, per spec aria-expanded should be undefined when; "The element, or another grouping element it controls, is neither expandable nor collapsible; all its child elements are shown or there are no child elements."