payments: rescan flag

[nkostoulas]

Requests are marked as payment complete if all payments succeed or if the coordinator is not set to handle doing the payments (but only collecting payment data) due to misconfiguration or other reasons. Add a rescan flag that goes through all previous requests and pays bids that have no payment txid. It is unclear though whether these have been paid in a different way and if they were, txids should be manually inserted.

[nkostoulas]

Only use case if coordinator initially set as non-payment in order to be switched later.