Bug: Multiple songs could be added to the jam with the same jamSongId

Since the timestamps used for the jamSongId when adding songs to the jam are not necessarily unique, so multiple songs could theoretically be added to the jam with the same jamSongId. 

This is a pretty minor bug and has a low likelihood of happening while we test. I don't really expect to fix this in the hours before the software fair so I'm just recording it here for posterity.
