api: fix return object for get_payment_methods call

This call is only used in the refreshPaymentMethods code path.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
api: export Litle specific-information in PaymentMethodPlugin

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
Merge branch 'master' of github.com:killbill/killbill-litle-plugin