Avoid scheduling two non-recorded talks at the same time

[edk0]

I think it would be nice (and hopefully not something the constraint solver struggles with) to penalize scheduling more than one non-recorded talk at a time.

I guess in theory this idea might be subsumed by a more general disappointment-minimizing scheme, but in practice not everyone hearts talks and also disappointments are somewhat less bad when you can watch a video.

I am happy to work on this myself, but am holding off for now because I heard the scheduling engine might be getting replaced.