[HUBZERO][#3468][COM_COURSES] use '-' if grade doesn't exist in CSV download
[HUBZERO][#3468][COM_COURSES] use '-' if grade doesn't exist in CSV download

anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms,zweidner/hubzero-cms,zweidner/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms