Invoice Expiry #419
Description
A consignment probably shouldn't block a transfer in a wallet forever in case a user doesn't want to accept it, or doesn't accept it in time.
An expiry will need to be non-optional so that it doesn't lock a user's wallet permanently.
The sender's wallet will then need to be able to unlock the capability to spend after invoice expiry, and also, the receiver should be able to get an error that their consignment is expired, and it should also provide how long ago it expired.