If the notification manager shuts down, sweepReqs channel is closed and sweepReq
object received from it becomes nil, causing panic in handleLoopInSweepReq. Now
this is fixed by checking if the channel was closed and if it was shutting down
loop-in manager itself.
If Run sets the current height field, it is technically a race between Run and
other methods reading the field. Setting in New is a safer option.
Removed a check that height is not 0 from static address manager.
This commit adds the listening for sweep requests from the server.
On a sweep request the loopin manager will fetch the loop in from the
db, do sanity and safety checks and then sign the psbt for the input
and send it back to the server.
