added more ARIA, including haspopup and aria-label

[mra11yx]

Did the following:

• added aria-haspopup to the example button and to any menuitem that spawns a submenu.
• commented out the title attr here because it duplicates the existing menuitem inner text, and won't be available without the mouse.
• hid icons from screen readers using aria-hidden
• used aria-label to provide more context to menuitems that go back a level
• added aria-label to icon menuitems since that will override any labeling weirdness that the inner text of the icon fonts could introduce