[Events 2.0] Ability to update payment status manually

Events 2.0 Beta lacks the ability to change the Payment Status or the number of tickets or items. 

Scenario: Registrant selects two of three available tickets and payment by check. After registration, the registrant wishes to purchase the third ticket and sends a check for three tickets. Event administration receives the check and cannot change the Payment Status from Pending to Paid or add the third ticket to the registration.