fixes #220

I still think this solution leaves a lot to be desired, but this is the best I could do for now while maintaining the existing design. I believe we should probably separate out the button that expands the menu and the buttons inside the menu, but this is a start.

1. I made all <span>s into role="button". (It was too difficult to make them true <button>s, but I would love a PR in the future to do that. ) 🙂 Because they aren't true buttons, we have to handle tabindex and keydown (enter/spacebar) ourselves.
2. I added aria-haspopup and aria-expanded to indicate when the menu button is opened.
3. I added a <section> with aria-label set to the i18n.skintext (default: 'Choose your default skin tone') so that it's easier to tell what this mass of <button>s is there for
4. I added aria-pressed states for when the skintone is selected/unselected to show that it's a toggle button
5. I added some text for each skintone button, via both aria-label and title so that you can hover to see them. This necessitated some new i18n defaults.

This is definitely not where I would like it to be long-term, but at the very least you can now tab to the button, press spacebar/enter to expand, and then tab through the expanded buttons and press spacebar/enter to expand those.