Also, some test refactoring and add servant-client to tests.

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`.

Basically, Gargantext.Prelude exports all of Protolude now.

It can be used to "bolt-on" policy checking into Servant API routes.

This is to prevent accidental updates of hyperdata with other JSON
structs.

This is safer than type Limit = Int

This is only the endpoint, it does nothing yet.