Removed field_extra_fields hook, and replaced it with standard field_create_field and field_create_instance calls in paypal_wps module

Backtracking slightly; subscription entities shouldn't be defined by csub core module, but with payment providers. Adding stub for paypal.

Issue #1307690 by webadpro: Allows subscription transaction types, working price structure and recurring status not saving.

Issue #1296120 by webadpro: Receiving IPN hits for cart type payments, and correctly setting the subscription ID from the IPN instead of -placeholder-

Code now conforms to coding standards better. Added functions to format prices nicely. Fixed error in rolereference module name

Switched from timings on subscription to timings on subscription recurrence entity. Period now in selectable D/W/M/Y, not seconds.