Add Cypress testing

[dangunter]

Fixes #17

Proposed changes:

• [x] Add Cypress config
• [x] Add a Cypress runner to CI
• [x] Add at least one sample test

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[dangunter]

Note that most of the files changed are either moved around a bit or added (to avoid downloading from CDNs). Future iterations should use a bundler at least for the JS to have fewer files to worry about

[lbianchi-lbl]

@CopyDemon will make a new PR containing only the Cypress changes.

[dangunter]

See comment above. New PR will be made