routing/router: persist payment state machine

This commit makes the router use the ControlTower to drive the payment
life cycle state machine, to keep track of active payments across
restarts.  This lets the router resume payments on startup, such that
their final results can be handled and stored when ready.

server.go

@@ -621,6 +621,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB, cc *chainControl,
 		Chain:              cc.chainIO,
 		ChainView:          cc.chainView,
 		Payer:              s.htlcSwitch,
+		Control:            channeldb.NewPaymentControl(chanDB),
 		ChannelPruneExpiry: routing.DefaultChannelPruneExpiry,
 		GraphPruneInterval: time.Duration(time.Hour),
 		QueryBandwidth: func(edge *channeldb.ChannelEdgeInfo) lnwire.MilliSatoshi {