Recurring contributions and auto-renew memberships: allow self-service and back-office update and cancellation

1. Allow authorized staff to cancel or modify a recurring contribution or an auto-renew membership from within CiviCRM back-office screens. Cancellation should update CiviCRM database recurring contribution status, insert an activity record, and optionally - for supported payment processors - use the processor API to send cancellation request to the processor. Updates should modify the CiviCRM recurring contribution record, insert an activity record, and optionally - for supported payment processors - use the processor API to send the change request to the processor.

2. Allow donors to cancel or modify a recurring contribution or an auto-renew membership from CiviCRM links which are included in each recurring contribution / auto-renew membership receipt.

Features Supported for Each Payment Processor
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Donors can cancel via API by clicking URL included in receipts: Authorize.net, Google Checkout, PayPal Pro
Backoffice staff can cancel via API from Cancel link on Recurring Contribution listing: Authorize.net, Google Checkout, PayPal Pro
Donors can cancel via PayPal site using link included in receipts (donor must log in to their own account): PayPal Standard
Backoffice staff can update recurring contribution status to cancelled. Subscription must be cancelled separately on processor website: All other processors

Donors can enter a new credit card and / or billing address by clicking URL included in receipts: Authorize.net, PayPal Pro
Donors can update the amount and # of installments by clicking URL included in receipts: Authorize.net, PayPal Pro
Backoffice staff can enter a new credit card and / or billing address by clicking Change Billing Details link from Recurring Contribution and Membership (auto-renew) listings: Authorize.net, PayPal Pro
Backoffice staff can update the amount and # of installments by clicking Edit link from Recurring Contribution listing: Authorize.net, PayPal Pro

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This is the parent task for this project. Additional details provided in sub-tasks.