multi: update WalletController PublishTransaction to include label

Add label parameter to PublishTransaction in WalletController
interface. A labels package is added to store generic labels that are
used for the different types of transactions that are published by lnd.

To keep commit size down, the two endpoints that require a label
parameter be passed down have a todo added, which will be removed in
subsequent commits.

breacharbiter.go

@@ -90,7 +90,7 @@ type BreachConfig struct {
 
 	// PublishTransaction facilitates the process of broadcasting a
 	// transaction to the network.
-	PublishTransaction func(*wire.MsgTx) error
+	PublishTransaction func(*wire.MsgTx, string) error
 
 	// ContractBreaches is a channel where the breachArbiter will receive
 	// notifications in the event of a contract breach being observed. A
@@ -566,7 +566,7 @@ justiceTxBroadcast:
 
 	// We'll now attempt to broadcast the transaction which finalized the
 	// channel's retribution against the cheating counter party.
-	err = b.cfg.PublishTransaction(finalTx)
+	err = b.cfg.PublishTransaction(finalTx, "")
 	if err != nil {
 		brarLog.Errorf("Unable to broadcast justice tx: %v", err)