GFOA\PDPoints

Added the PDPoints class, which encapsulates PD points logic (i.e. determining when PD points are expired, and accordingly how many are available to a given organization/person).
Payment Display

Added methods to the GFOA\Organization and GFOA\Person classes to allow payment history to be retrieved.

Added and integrated the payment.phtml template into the People and Organizations controllers.  This template displays payment history -- including a total number of PD points -- on the page of each organization and person.