Offline Participant Registration : Retrieve default confirmation email message from online confirmation email as configured for the event

In 2.0, we retrieved and saved values to the event record when a message was entered for the confirmation email (offline event registration). This had the potential to cause problems because a "personal message" - specific to the participant - was often entered and then saved / retrieved for the next participant registration.

Rather than do this, we'll retrieve the configured confirmation email text as a default message (as set in Online Registration settings for the event).