Now everything is in Core/Config

This was (User, Either CorpusName, [CorpusId]) before, but the case of
UserMaster doesn't make sense with these parameters, so I rewrote the
function to accept only correct datatypes as inputs.

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.

This important commit introduces the 'DbCmd' constraint set, allowing DB
functions to require only a connection pool and some `GargConfig`.