server+contractcourt: signal channel fully resolved

We might want to react to a channel being fully resolved after being
involved in a force close. For this we add a new callback and invoke it
where appropriate.

server.go

@@ -1004,6 +1004,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		Sweeper:                       s.sweeper,
 		Registry:                      s.invoices,
 		NotifyClosedChannel:           s.channelNotifier.NotifyClosedChannelEvent,
+		NotifyFullyResolvedChannel:    s.channelNotifier.NotifyFullyResolvedChannelEvent,
 		OnionProcessor:                s.sphinx,
 		PaymentsExpirationGracePeriod: cfg.PaymentsExpirationGracePeriod,
 		IsForwardedHTLC:               s.htlcSwitch.IsForwardedHTLC,