Test the frontend with Cypress

[Morriar]

@geffrak and myself have been playing around with https://www.cypress.io/ and managed to set it up and test our login on staging.

It would be cool to push it further.

TODO:

• Have a way to build locally the app
• One-liner to run the tests with cypress
• Isolation for tests (db cleans for example)
• Find a way to record actions from browser
• Integrate with CI
• Find a way to export videos without paying too much