set up accessibility tests/assertions in CI using aXe (WCAG 2.1)

[chris48s]

Public sector websites must conform to WCAG 2.1 by September 2019 and most of our users are in local government. Our widget should meet these standards.

• Read
  • https://www.w3.org/TR/WCAG21/
  • https://reactjs.org/docs/accessibility.html
• Evaluate where the gaps are
• Fix them
• Investigate tooling that can help us audit/fix problems. e.g: https://github.com/dequelabs/react-axe
• Test the widget with a screenreader - am I right that the react component lifecycle doesn't tell the screenreader that the page content has changed, or am I making this up?

[chris48s]

Mostly covered in #279

TODO: set up accessibility tests/assertions in CI using https://github.com/nickcolley/jest-axe

[Bekabyx]

react-axe now deprecated - repackaged as https://github.com/dequelabs/axe-core-npm/tree/develop/packages/react instead. We may be able to use Lighthouse instead/as well.