regrade: support unicode (fix #2446)

Support unicode names by just manually forcing things to ASCII output.
Seems like a blunt tool, but oh well.  It's just for logging.

Also we weren't handling the case where we were creating ExamRecordScore
or ExamScore rows.  Those rows were getting created, but those new
records have id=None, and that just causes printing problems.  So fixing
that too.
Merge pull request #2447 from Stanford-Online/sef-2446-regrade-python

regrade: support unicode (fix #2446) -- MASTER