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

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

Merge remote-tracking branch 'origin/337-node-phylo-export-the-phylo-in-json-and-dot-format' into dev

This big commit adds a separate module hierarchy for Servant named
routes (see https://www.tweag.io/blog/2022-02-24-named-routes/ ) which
will make working with servant endpoints more pleasant (especially when
it comes to emitted errors).

This still doesn't do anything to wire the routes to the concrete
handlers.