Added content for Refunds tab when refunding all tickets is unavailable
Established generic payment method stub for sending a refund request
Abstracted PayPal-specific refund-all logic out of main class
Fixed several minor errors that prevented refund-all batches from succeeding
Refactoring payment_refund() and send_refund_request() for DRY-ness
Moved payment result log from PayPal module to main class

It's better to have logging in the main class, rather than individual modules, because we can't trust that 3rd party modules will do logging, and it's redundant to have the logging in each individual module.
Tracks status of refund batches and displays result to user
Refreshing i18n strings