Multiple Event Registration

Allows Admins to set up a 'main/parent' event with some 'related/child' events, such that registering for the 'main/parent' event also registers the participant to all the 'related/child' events.

Set up involves specifying the Event ID of the 'main/parent' event in the custom field on the 'related/child' events.

Such registrations can then be overridden if necessary by admin, eg if a user signs up for an event series E1, E2, E3 etc, but are then unable to attend E3, they can be instead registered for F3 for example