Allow event organizers to create advanced discount/validation rules based on attributes of either an attendee or the order.

Use case 1

As an event organizer, I want to be able to give a discount to members of my organization. If an attendee has the member attribute, they should be given a discount.

Use case 2

As an event organizer, I want to be able to give a discount for families registering. If an attendee has selected two adult tickets, they should be given a discount. They also should not be able to select a child ticket unless there are two adult tickets.