Apply WAI-ARIA to the Backpack

[stenington]

I think we'd benefit from someone with a solid understanding of WAI-ARIA going through and marking up the Backpack as appropriate, although that might actually be a significant chunk of work. Nevertheless, I don't know enough right now about WAI-ARIA to make smaller tickets.

[threeqube]

As @cmcavoy mentioned, let's not get bogged down by the deets. Most important thing is to get that VPAT form up there and we can continue to work on the details of 508 implementation even past v1.0 release.

[cmcavoy]

@threeqube I also asked @stenington to document the changes we'd need to make if they were fresh in his head. All the accessibility tagged items are backlogged until 1.0 is done. The only accessibility 1.0 issue is #477

[threeqube]

👍