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

It also improves the error in case it's the first time we are running
the tests and we have no coreNLP service running.

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.