Updates Mark's talk to a panel

Note that I extended the length of Mark's panel. I don't think 30 minutes is enough time for this, and it seems like it will be very interesting especially if he's collecting questions via Twitter beforehand. I debated moving it to another day or allowing it to go long, but this seems like the best solution since the Bluebird will be arriving at 4:45pm. Everyone will still get a 15 min break after Dan's talk, so it doesn't seem like it would be a big deal to have one break that is short.