It's better to enumerate fields than not - easier to search later.

Also, a performance improvement for queryNgramsOccurrences (no VALUES).

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.