Added export fields to EventAttendee, and removed failover constructor magic
Added print / export buttons to attendees grid.
Moved grid generation to its own function.
Created a `getValidAttendees` function for getting the attendees that have been successfully registered for the event.
Minor tidies.
Added `getRegistrant` function to EventRegistration to provide a summary of the person who did the registration
Various minor code tidies
Updated EventUnregisterController to use new data model
Created class for handing emailing registrations