Add a11y testing

[xmunoz]

Fixes #1691 .

[xmunoz]

We're going to take a manual testing approach for now.

[colinxfleming]

let's keep this open for one more day - want to try something with this as a base

[colinxfleming]

@xmunoz had a sec to take a pass at this and here's the output - the routing_test (the more straightforward capybara test we have) now has an assert_accessible page in it. (Goofily, since rails 6 or so, integration tests have been more 'post a payload to this endpoint', and system tests have been the 'load up your browser' tests.) Definitely a gotcha, but assert_accessible should cooperate now.

sorry for some of the gemfile regressions. I think probably drop and redo the merge commit there.

[xmunoz]

Sweet, thanks!

[xmunoz]

One of the a11y violations was fixed by upgrading bootstrap_form. Unfortunately, this package upgrade also causes some of the integration tests to fail. There is only one other violation remaining, and the fix looks pretty straight-forward.

[xmunoz]

After more investigation, I'm not sure how to fix the other a11y concern. It specifically concerns missing table header text for the following scenarios.

We are using those header spaces for layout. The elements in these column are icons which are hidden from aria, meaning they are invisible to screen readers.