It also improves the error in case it's the first time we are running
the tests and we have no coreNLP service running.

Added more tests for more subtle cases.

This is a first stepping stone in avoiding bugs by having `UserId` and
`ContextId` being proper types, and not synonyms.

We also refactor things to have `AuthenticatedUser` carry the `UserId`.

Tests were written with a very flat module hierarchy which made them
a bit confusing to navigate. This commit moves everything under a common
`Test.*` hierarchy.

Alas I (Alfredo) had to split the runners for tasty and hspec because in
tasty we cannot control explicitly the level of parallelism, but for the
DB stuff we need sequential tests, whereas for the Jobs tests we need
parallelism, or rather the executable to be compiled with `-threaded`.