This allows us to have only one single (static) map which will be
treated by GHC as a CAF.

We do that thanks to a new typeclass method for
the `MonadJobStatus` called `noJobHandle`.

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.

Also, refactored NodeStory to use Prelude database.

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