Refactor balloon interface to also handle prints

[vmcj]

When you print via DOMjudge it makes sense to also handle marking done via the balloon interface,

So refactor the balloon handout to handle different "task types: {balloon,print}" and let someone filter on those, storing the filesize, begin & endtime to detect possible queuing issues.

This also gives some nice statistics on correlations between teams which print versus their performance.