send message to user to complete bitpay tx

[radiumsoup]

when a btc-denominated buy transaction is placed, store a password-encrypted presigned transaction on the server. (password is not necessarily related to the passphrase) When there is a match to that order, send a message to a user's email or SMS with a UUID link that accesses (server-side) the stored signed transaction in encrypted form. User is prompted for the password to decrypt that stored transaction - when entered properly, the signed transaction is decrypted and broadcast, paying the bitpay tx on behalf of the user. If user does not know or cannot recall the password, link to an option to log on to the full site with their passphrase to see pending matches and handle the tx manually as is already in place.