lnrpc: display transaction label in transaction details

lnwallet/btcwallet/btcwallet.go

@@ -519,6 +519,7 @@ func minedTransactionsToDetails(
 			TotalFees:        int64(tx.Fee),
 			DestAddresses:    destAddresses,
 			RawTx:            tx.Transaction,
+			Label:            tx.Label,
 		}
 
 		balanceDelta, err := extractBalanceDelta(tx, wireTx)
@@ -564,6 +565,7 @@ func unminedTransactionsToDetail(
 		Timestamp:     summary.Timestamp,
 		DestAddresses: destAddresses,
 		RawTx:         summary.Transaction,
+		Label:         summary.Label,
 	}
 
 	balanceDelta, err := extractBalanceDelta(summary, wireTx)

lnwallet/interface.go

@@ -103,6 +103,9 @@ type TransactionDetail struct {
 
 	// RawTx returns the raw serialized transaction.
 	RawTx []byte
+
+	// Label is an optional transaction label.
+	Label string
 }
 
 // TransactionSubscription is an interface which describes an object capable of