This commit starts adding the conversion functions from a
`BackendInternalError` to a `FrontendError`.

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.

We now require CoreNLP listening on port :9000. We will have to find
a way to spin that up in CI as well.