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.

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

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.

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

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

This is safer than type Limit = Int

They are changed to MaybeFields ...Read instead when joining.

Remove joins, use optionalRestrict instead.

Also, remove cabal.project because stack.yaml and package.yaml cover
dependencies already.