user RSVPs after event is finished.

[jaredwould]

Lindsay Saunders signed up for Villagecraft's Birthday Party! on 11/24 -- 12:20PM, two days after event end.

I canceled my own attendance and was able to sign up also for this expired event.

Let's not allow users to sign up for events that have all ready happened. Let's close signups when event starts. Also, once event has started, replace the SignUp button with a button that has the old date. If someone tries to click it, it can give a simple pop up "______ all ready happened."