AUI-1363 - Make aui-redo accessible

Hi @drewbrokke,

This one is working great.  But now I think we need to abstract out the accessibility logic into its' own file.  @Robert-Frampton recommended we use aui-modal-resize as an example for an augmentation class.  I think we could call ours aui-undo-redo-accessibility.   And once we do that, we also need to write a test case/cases.  Could you tackle these when you get a chance?

Please let me know if there are any issues.

Thanks!