Implement UI driven integration test suite

[franckc]

We should implement an automated UI driven test suite for dshop and for the deployer. The focus should be on testing critical flows (checkout, shop creation, shop publish, ...).

The main goal being to catch regressions when merging in a new PRs. This would save tons of time when reviewing new contributions to the dshop repo.

Ideally those automated tests would run as part of the GitHub flow for submitting PRs.