Jbau penalties to float

@jrbl or @sefk 

tested data migration on staging and had to make sure that it doesn't use too much memory, while not making too many sql queries.  iterating on the solution resulted in the last 6 commits

I think this is a decent spot.  The migration did take about 7-8 minutes to run on staging, but it worked on previously wrong scores, and taking a late quiz now (e.g. XML quiz) correctly applies late penalty.