A11y snapshot tests

[Mattsi-Jansky]

I'd like my site to be accessible, and it probably isn't right now (webaccessibility.com gives a score of 81%, for whatever that's worth). I'd like to make A11Y evaluation part of my build pipeline as snapshot tests, ensuring that deploys aren't completed if the evaluation score lowers. That way I can keep track of site accessibility, ensure it doesn't regress, and iteratively improve it.