AUI-1364 - Make aui-toggler accessible

Hi Marc,

Attached is another update for https://issues.liferay.com/browse/AUI-1364.

Blind people should now know the toggle state too haha.

So I ended up adding role=button on all headers.  Without it, if the header isn't actually a button, it won't read the expanded/pressed state.  Also I added the aria-hidden attribute to content when it is toggled.

Please let me know your thoughts.

Thanks!