Related MR:
!378

Also, some small refactorings.

Related to
#418

These types are the same, except for Database.Empty

I managed to have backwards compatibility with the frontend format,
hence the frontend doesn't need any changes.

This simplifies the WithQuery structure even more

Also, add WithQuery pubmed test (with api_key)

There is now only a 'datafield' field, no need for duplicated
'database'.

Related to #441

[graphql] fix droping field prefixes

See merge request !379

It wasn't used anyways.

I want to understand ngrams algorithms better.

Upgrade 'haskell-bee' version, also bump up versions of some packages

See merge request !377

Resolve "Fix test build warnings"

See merge request !376

Also, add -Werror to tests so that no warnings in tests are reported anymore.