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

Also, some test refactoring and add servant-client to tests.

This commit modifies the backend code to convert the input CSV into an
`NgramsList`, so that we can reuse the JSON API for the upload.

it also brings the CSV and JSON APIs closer in look.
Temporarily disable the `importCsvFile` function.

This commit makes possible to pass an optional `X-Garg-Error-Scheme`
header in a client request to enable the new error format.

This commit introduces a new DB function called `isSharedWith`
that can be used to check for team/public/private nodes and their
shared resources.

This commit partially undo the access policy checks for the
GraphQL endpoints, until we find a better story to correlate
the `user_id` we sometimes receive with the info from the
`AuthenticatedUser`.

It can be used to "bolt-on" policy checking into Servant API routes.