Adding Cancel/Refund button to Edit Attendee Info form
Reverting 53dca1c63cf8d1b41c68693aa18e9f73f5269f31 because it wasn't necessary
Prepping CampTix_Plugin for abstracting refunds into CampTix_Payment_Method
Creating stubs for payment refund methods
Updated existing user-requested refund code to work with payment module architecture

The code for issuing user-requested refunds via PayPal was originally built into the main CampTix_Plugin class. Later on, the architecture was refactored to allow for multiple payment gateways via extending the CampTix_Payment_Method class.
This commit abstracts the refund code in CampTix_Plugin and updates CampTix_Payment_Method and CampTix_Payment_Method_PayPal to use adhere to the new architecture.