Override GraphQL API for integration tests

Created by: felixfbecker

This adds the overrideGraphQL() and waitForGraphQLRequest() we had sketched out in our trigramming session. This passes for the settings test, but the search tests don't use the API yet. I started with using our existing GraphQL types, which is not very ergonomic and needs a lot of casting.

My main take-away from working on this is that specifying manual responses for every test will not scale. It was extremely annoying even just for a single test. We should therefor investigate the dynamically generated responses.

Minor addition: I added support for .skip() and .only() like in Mocha, because that was annoying to not have.

This also contains some fixes to the settings test we had drafted up, which didn't work yet.