Add disabled styling to InlineMenuWidget

The menu as a whole can be diabled, or specific options. Add
greyed-out styling to apex, and cursor:default to core styles.

Change-Id: I0d1c8cf5b8c1d98e24b7c23109f802da4850a559
Promote zIndex of InlineMenuWidget options list

Otherwise the dropdown will appear under other widgets (see
the widgets demo as an example).

Change-Id: I1c3d35986fa0a6affad5e81c478ab14acee9128b
Merge "Add disabled styling to InlineMenuWidget"
Merge "Promote zIndex of InlineMenuWidget options list"