AUI-1349 - Make aui-carousel accessible

Hi @Robert-Frampton,

Attached is an update for https://issues.liferay.com/browse/AUI-1349.

I migrated my changes to a new file, 'aui-carousel-accessibility.js', using 'aui-modal-resize.js' as an example.

Please let me know if there are any issues.

Thanks!