Happy Business Starts Here

Subscription creation and update endpoints should return ids of any created invoices

The Update Subscription endpoint has an option to generate an invoice for the subscription.  However it doesn't return the id of any generated invoices.  Subsequent API actions to that invoice are more difficult.  If the id was returned, then we could easily call the collect endpoint to collect payment.  We don't currently execute the collect at the same time as the invoice generation because all actions are wrapped in a transaction.  In that case, if the payment fails, then the invoice AND the subscriiption is rolled back.  We want the subscription and invoice to stay if the payment fails.