contractcourt+lnrpc+lnd: s/BreachArbiter/BreachArbitrator

Since we have two other examples of XArbitrator, we rename
BreachArbiter to BreachArbitrator to keep things consistent.
The aim is to reduce the amount of lore you need to know to
intuit where things are or what they do.

contractcourt/chain_watcher.go

@@ -175,7 +175,7 @@ type chainWatcherConfig struct {
 
 	// contractBreach is a method that will be called by the watcher if it
 	// detects that a contract breach transaction has been confirmed. It
-	// will only return a non-nil error when the breachArbiter has
+	// will only return a non-nil error when the BreachArbitrator has
 	// preserved the necessary breach info for this channel point.
 	contractBreach func(*lnwallet.BreachRetribution) error
 
@@ -1243,14 +1243,14 @@ func (c *chainWatcher) dispatchContractBreach(spendEvent *chainntnfs.SpendDetail
 		closeSummary.LastChanSyncMsg = chanSync
 	}
 
-	// Hand the retribution info over to the breach arbiter. This function
+	// Hand the retribution info over to the BreachArbitrator. This function
 	// will wait for a response from the breach arbiter and then proceed to
 	// send a BreachCloseInfo to the channel arbitrator. The channel arb
 	// will then mark the channel as closed after resolutions and the
 	// commit set are logged in the arbitrator log.
 	if err := c.cfg.contractBreach(retribution); err != nil {
 		log.Errorf("unable to hand breached contract off to "+
-			"breachArbiter: %v", err)
+			"BreachArbitrator: %v", err)
 		return err
 	}