(no default getCurrentTime anymore)

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.

FlowCmdM -> DBCmd or HasNodeStory is usually enough

- DBCmd instead of Cmd
- remove FlowCmdM in favor of HasNodeStory

This fixes commit 5d5300cd which
automatically changed all 'return' to 'pure' in our code, resulting in
broken SQL etc.

The issue was that when search was performed, the initial table didn't
have an archive ready and so first commit resulted in some errors on
the frontend. This fix performs the commit after flow is finished.

This commit refactors the codebase to add a new function called
`addDocumentsToHyperCorpus` which generalises the common pattern of
calling `insertMasterDocs` and later adding the documents via the DB
`Doc` functions.

It also "lowers" some functions to run into a plain `DBCmd`.

Fixes #258

This commit fixes the issue of the "empty Ngrams". The culprit was a bug
in the `arxiv-api` package, which was fixed by:

gargantext/crawlers/arxiv-api!2 (commits)

In a nutshell, due to the fact the relevant `Conduit` was never
completing, it was blocking the `flow` function, which was endlessly
waiting for the last part of the results to arrive.

Hence we were never calling the `flowCorpusUser`, which is the function
responsible for generating the Ngrams.

Also, use ISO639 languages in some places.

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

The bug was introduced in

gargantext/haskell-gargantext!177 (diffs)

It caused hyperdata to be updated with whole corpus, serialized, hence
hyperdata inside hyperdata.