Implement front-end testing

We have wanted to do front-end testing for a while, and there are some updates:

We have successfully used jest for React testing successfully in another repo, including the pattern of sharing example API JSON between the frontend and backend. It's a little bit different because the other repo uses Redux, and primarily what we are testing are the actions. We could still reproduce something like that here without Redux, it just wouldn't look quite the same way (or we could start using Redux).

We have also successfully used selenium and nightwatch for acceptance/click testing, that would be pretty useful to include here.

No files, tests, or entry points are named. Start by reviewing the existing frontend structure and the prior repository's Jest approach, then compare Jest/React testing with Selenium and Nightwatch; done means the project has an agreed testing approach and working frontend and acceptance-test coverage.

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