Integrate nightly reconciliation for payment processors

Most payment processors offer a nightly audit log, which includes a record of every transaction or subscription change on your account. Providing this functionality would greatly improve robustness, and prevent lost payments.

See https://github.com/wikimedia/wikimedia-fundraising-tools/tree/master/audit/paypal and https://github.com/wikimedia/wikimedia-fundraising-tools/tree/master/audit/worldpay for working examples of this kind of system.

To integrate this feature into CiviCRM, a nightly cron script would fetch audit logs, parse, and enter missing contributions/contacts into the database. Email notification could be configured when the script fails, or when lost transactions are picked up. This could also be used like a checkbook is balanced, and existing contributions could be tagged as positively confirmed.