Allow PhortuneTestProvider to add payment methods
Summary: Provide a bare implementation so that you can add PhortuneTestProvider as a payment method. Ref 2787.
Test Plan: Added "cards" through the test provider.
Reviewers: btrahan, chad
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2787
Differential Revision: https://secure.phabricator.com/D5772