[WIP] integration test for simple_theme integration
This PR is done to activate CircleCI build and check whether a new test runs or not, and to improve it progressively until CircleCI says it runs.
Done as part of https://tasks.opencraft.com/browse/OC-3259 This PR will be closed after the test runs, and the changes incorporated to the main PR (https://github.com/open-craft/opencraft/pull/235)