Command format: close id [unilateraltimeout] [destination]
Close the channel with peer {id}, forcing a unilateral
close after {unilateraltimeout} seconds if non-zero, and
the to-local output will be sent to {destination}. If
{destination} isn't specified, the default is the address
of lightningd.
Also change the pylightning:
update the `close` API to support `destination` parameter