Add cypress testing

Addresses #111 (closed)

Add cypress.io testing to the project.

Cypress.io advantages:

1. Fairly easy to write.
2. Committed CI/CD, esp. Gitlab.
3. Also covers unit testing.
4. Not one of the big ones.

Disadvantages:

1. Not standards compliant.
2. Uses jquery.
3. Cannot close and launch browsers.
4. Single source company, so the license might change.