Add "Filled" filter to the Event Catalog

[jducoeur]

A common (I think) use case for the Event Catalog is to see what I've marked as interesting, to decide my next-round signups.

This currently has a "Favorite" filter, which is great. It would be helpful to also have a "Filled" one which, when turned off, would hide all games that are currently full. (And therefore are only candidates if I'm prepared to waitlist for them -- which usually means I already had them top-of-mind anyway.) This would help reduce the scope, especially during later rounds, and reduce the brain-burn of deciding which game to shoot for.