Allow picking dedupe rule per event

This follows the changes for CRM-14134 moving to using the Unsupervised rule for matching all event participants.

That moves away from using email only if the "Allow multiple registrations from the same email address" is not checked and using the Supervised rule for additional registrations when that box is checked. Although those are questionable choices, the principle of being able to use different rules for different situations is a good one.

This will also alter the changes in CRM-14540 to check whatever rule is in use against the fields that are being collected.