lnwallet: add a BtcWallet implementation of WalletController

This commit adds the first concrete implementation of the
WalletController interface: BtcWallet. This implementation is simply a
series of wrapper functions are the base btcwallet struct.

Additionally, for ease of use both the BlockChain IO and Signer
interface are also implemented by BtcWallet. Finally a new WalletDriver
implementation has been implemented, and will be register by the init()
method within this new package.

lnwallet/btcwallet/driver.go

@@ -0,0 +1,45 @@
+package btcwallet
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnwallet"
+)
+
+const (
+	walletType = "btcwallet"
+)
+
+// createNewWallet creates a new instance of BtcWallet given the proper list of
+// initialization parameters. This function is the factory function required to
+// properly create an instance of the lnwallet.WalletDriver struct for
+// BtcWallet.
+func createNewWallet(args ...interface{}) (lnwallet.WalletController, error) {
+	if len(args) != 1 {
+		return nil, fmt.Errorf("incorrect number of arguments to .New(...), "+
+			"expected 1, instead passed %v", len(args))
+	}
+
+	config, ok := args[0].(*Config)
+	if !ok {
+		return nil, fmt.Errorf("first argument to btcdnotifier.New is " +
+			"incorrect, expected a *btcrpcclient.ConnConfig")
+	}
+
+	return New(config)
+}
+
+// init registers a driver for the BtcWallet concrete implementation of the
+// lnwallet.WalletController interface.
+func init() {
+	// Register the driver.
+	driver := &lnwallet.WalletDriver{
+		WalletType: walletType,
+		New:        createNewWallet,
+	}
+
+	if err := lnwallet.RegisterWallet(driver); err != nil {
+		panic(fmt.Sprintf("failed to register wallet driver '%s': %v",
+			walletType, err))
+	}
+}