But they still don't work because there is no HasClient implemented
for the websocket server.

This makes it easier to change protocols, ports etc.

This beefy commit removes the old (unnamed) Servant API.

This big commit ties the knot with the named _routes_ by providing
concrete server (i.e. handlers) implementations.

Also, will use stm containers

Merge branch '345-docs-tsv-export-import-check-and-maintain-consistency-between-export-and-import-formats' of https://gitlab.iscpif.fr/gargantext/haskell-gargantext into 345-docs-tsv-export-import-check-and-maintain-consistency-between-export-and-import-formats

I'm currently able to do the following:
- start gargantext-server (as it hosts central exchange and
dispatcher, currently)
- start a websocket connection:
  websocat ws://localhost:8008/ws
- subscibe to a topic (in websocat):
  {"request": "subscribe", "topic": {"type": "update_tree", "node_id":
  15}}
- optionally subscibe to other node_ids or start other websocat's with
  different subscriptions (can be multiple)
- fire up
  cabal v2-run gargantext-central-exchange -- client
  This triggers a node_id: 15 and node_id: 16 notification to be sent

You can send your own notifications, e.g. with Python:
import json
import nanomsg as n
s = n.Socket(n.PUSH)
s.connect('tcp://localhost:5560')
s.send(json.dumps({'type': 'update_tree_first_level', 'node_id': 15}))