Revert "Fix an error when getting results from DB in get_student_groups."

This reverts commit 946ea39f0ceb52f45328f53e8d21d84310f94a4e.

The commit fixed the problem in the old versions but introduced it
in the new versions. Another kind of fix is needed so that
it works always.
Alternative fix for the error in get_student_groups.

The previous fix introduced the error in the newer versions
of python/SQLite, which were previously unaffected.

The berst solution right now is using the column indexes instead
of the text keys.
Update version number to 0.4.4 and changelog.
Merge branch 'hotfix-0.4.4'.