Have a more reliable testing of configs

[tomasciccola]

When testing config import on the frontend, we have grab fixtures from this repo, zip them and import them on CoMapeo. This has shown issues when importing (mostly import not working but not showing any errors nor warnings).
I think this is a somewhat brittle way of testing, since the fixtures are created with a different method than configs themselves.
Maybe the fixtures should be created as unbundled configs (like config repos) and built for testing using the settings-builder itself.
This would give as better reliability for testing configs and avoid pitfalls that are hard to debug