Issues with self service cancelling and transfering event bookings with multiple participants

A couple of issues with the self service event booking facility : CRM-16761

1. Following the self service links to cancel or transfer an event booking only provides the option to effect the lead booker and not the guests. This leaves guests in the system with registered status even though they are actually not coming. Ideally the self service link should have the option to cancel all guests.

1. Transferring a booking with guests transfers the lead booker registration to the new account (automatically matching on the first record it finds with the same email address (which may be another problem)) but it leaves the guests attached to the original booker (who now has the status of transferred) who isn't coming. Ideally there should be an option to transfer the guests as well.

1. Transferring a booking should also be an optional feature as you may want to allow cancellations but not transfers as the events may be (for example) invite only.