Bump plugin version to 0.2.2.  Add unit test for PinPaymentService.addStoreCredit().  Delete any subscribers created during tests right after the test.
Cleaned up tests.  Went back to deleting the whole test site before each test.
Changed PinPaymentsService method signatures to accept a String customerId instead of a long because the pin payments api doesn't put any such restriction on it and in some situations customer id's may go beyond a long's MAX_VALUE.  Bumped plugin version to 0.2.4.