* add prettier and have it format all js code except website:
:
* trying running prettier check in CI
* fix runs on in CI
* change CI job name
* fix prettier erros and fix CI
- Move from Mocha to Jest for JS testing (Jest seems to have better support for
'watching' tests and a more active community these days).
- Codemod existing tests to Jest syntax (using https://github.com/skovhus/jest-codemods)
- Fix some errors in tests that were previously hidden.
- Update Babel.
