Implement missing CSV multicolumn tests.

Test should just import multicolumn CSVs without error, and the test should check if all wanted data and columns are imported.

As testdata should be used:
mittagqi_meta/git/testdata/editorTestfiles/public/CSV-with-muliple-target-alternatives.csv

(above CSV should be the same as in https://confluence.translate5.net/display/BUS/ZIP+import+packages%3A+Examples?preview=/1245705/1245699/example-task-CSV-with-muliple-target-alternatives.zip, if not use the one from confluence.)