Alert front-end when number of checkins > venue seating count

[AbhiAgarwal]

When the number of people checked in exceeds the seating count for that particular event we should alert the front-end. This is good in terms of design because it helps the person checking in know that this event is now full, and we should stop people from checking in!

This doesn't have to be done during startup-week, but would be a great enhancement! I constantly look at tnyu.org to see if the number has been exceeded, but this would help fix that!