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/breach_resolver.go

@@ -8,13 +8,14 @@ import (
 )
 
 // breachResolver is a resolver that will handle breached closes. In the
-// future, this will likely take over the duties the current breacharbiter has.
+// future, this will likely take over the duties the current BreachArbitrator
+// has.
 type breachResolver struct {
 	// resolved reflects if the contract has been fully resolved or not.
 	resolved bool
 
 	// subscribed denotes whether or not the breach resolver has subscribed
-	// to the breacharbiter for breach resolution.
+	// to the BreachArbitrator for breach resolution.
 	subscribed bool
 
 	// replyChan is closed when the breach arbiter has completed serving
@@ -42,8 +43,8 @@ func (b *breachResolver) ResolverKey() []byte {
 	return key[:]
 }
 
-// Resolve queries the breacharbiter to see if the justice transaction has been
-// broadcast.
+// Resolve queries the BreachArbitrator to see if the justice transaction has
+// been broadcast.
 func (b *breachResolver) Resolve() (ContractResolver, error) {
 	if !b.subscribed {
 		complete, err := b.SubscribeBreachComplete(