allow for registrants to be added to completed registrations
When making additional payments, and the minimum deposit is not set (requiring full payment)
 - combine previous payments with the current amount when factoring minimum deposit (minimum deposit is the total cost now)
 - the radio button amount should be the remaining balance, not the total due
Merge pull request #267 from CruGlobal/EVENT-140

allow for registrants to be added to completed registrations