AUI-1527 - add base keyboard navigation

Hi Eduardo,

Based on your recommendation to Marc in this pull: https://github.com/eduardolundgren/alloy-ui/pull/618,  I leveraged the NodeFocusManager plugin for handling focus in the header.

I also included the aria-labels and roles in this pull for the buttons in the header.

Please let me know if there are any issues.

Thanks!