[Events 2.0] Add Guest option that does not require a separate ticket

We need to have the ability to register a guest in our events on our side that doesn't take us through the full customer sequence of checkout. There are pleanty of times when guests have a credit, pay cash or have a gift/comp ticket and there is no easy or simple way to add them to registration. In the old system there was a way, it was a multi step way, but it could be done, now you can't. 

Please fix this.