WIP: upload CSV file for cohorting students

@cahrens: I found a bug in `unicodecsv.DictReader` where it throws a `TypeError` when opening an empty file (`csv.DictReader` does not fail on this input). Since we just need the header row in this case, I replaced it with `unicodecsv.reader`.

I'm also working on a PR to fix the bug in the unicodecsv library.