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/channel_arbitrator.go

@@ -860,7 +860,7 @@ const (
 
 	// breachCloseTrigger is a transition trigger driven by a remote breach
 	// being confirmed. In this case the channel arbitrator will wait for
-	// the breacharbiter to finish and then clean up gracefully.
+	// the BreachArbitrator to finish and then clean up gracefully.
 	breachCloseTrigger
 )
 
@@ -2891,7 +2891,7 @@ func (c *ChannelArbitrator) channelAttendant(bestHeight int32) {
 			}
 
 		// The remote has breached the channel. As this is handled by
-		// the ChainWatcher and BreachArbiter, we don't have to do
+		// the ChainWatcher and BreachArbitrator, we don't have to do
 		// anything in particular, so just advance our state and
 		// gracefully exit.
 		case breachInfo := <-c.cfg.ChainEvents.ContractBreach:
@@ -2926,7 +2926,7 @@ func (c *ChannelArbitrator) channelAttendant(bestHeight int32) {
 			}
 
 			// The channel is finally marked pending closed here as
-			// the breacharbiter and channel arbitrator have
+			// the BreachArbitrator and channel arbitrator have
 			// persisted the relevant states.
 			closeSummary := &breachInfo.CloseSummary
 			err = c.cfg.MarkChannelClosed(