Sync with changes to the encapsulated version for zc220+

[lat9]

Syncing with the encapsulated version of the payment-module for zc220+ (zencart/zencart#7515)

• pprAutoload.php is now loaded via the admin/catalog observers.
• PHP define (FILENAME_PAYPALR_MODULE) created in the catalog observer pointing to the 'base' payment module.
• Correct misplaced parens on zen_redirect calls in ppr_listener.php.
• Update WebhookResponder doCrcCheck to return null if posted results are necessary.