Remove selection of tickets from time-critical sales path

[russss]

People who want to buy more types of ticket are at a disadvantage in public ticket sales, because tickets aren't reserved until you select your tickets and click the button. This is becoming increasingly problematic.

I think basically the two options are:

1. Reserve a chunk of capacity after initially starting the ticket sales process, or
2. Allow people to pre-select their tickets before ticket sales start

I fear both of these mean that we need a queueing system.