Arbitrary level locking

[yurloc]

It is often the case that we want to optimize very locally because the schedules are already distributed, but then a juror does not show up. If not only rounds but individual rooms or even each juror could be fixed this would help a lot in these cases.

[yurloc]

It is already possible to lock individual jurors. However, locking seems to totally broken at this moment. This needs to be fixed in the 2016 release (i.e. tomorrow).

[yurloc]

Depends on #40.