KeyNav updates

Add focusChildren = false mode for ComboBox, refs ibm-js/deliteful#331,.
Also has a bunch of renaming, fixes #304.

Replaces PR #302.
But still, this constraint is a painful drawback, isn't it? In practice, it would require the List to set ids on its items (better than having the ComboBox doing it from the outside of the List, I would say), and doing so only for the sake of the ComboBox using KeyNav's focusDescendants == false mode... Anyway, before deciding on it I think we need to double-check if the aria-activedescendant attribute is doing the trick - if it doesn't, no need for ids.