AUI-1349 - Make aui-carousel accessible

Hi @Robert-Frampton

Attached is an update for https://issues.liferay.com/browse/AUI-1349.

Note:  Just a heads up, while testing this one out I discovered a bug (https://issues.liferay.com/browse/AUI-1578) that becomes very easy to replicate with key controls.  If you hit left or right, and then quickly hit the opposite direction, the carousel will be hidden for a short period.

Please let me know if there are any issues.

Thanks!