Code review for new payment work

Conflicts:
	beatrix/src/test/java/org/killbill/billing/beatrix/util/AuditChecker.java
	beatrix/src/test/java/org/killbill/billing/beatrix/util/PaymentChecker.java
	beatrix/src/test/java/org/killbill/billing/beatrix/util/RefundChecker.java