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/blockchain.go

@@ -0,0 +1,55 @@
+package btcwallet
+
+import (
+	"encoding/hex"
+
+	"github.com/roasbeef/btcd/wire"
+)
+
+// GetCurrentHeight returns the current height of the known block within the
+// main chain.
+//
+// This method is a part of the lnwallet.BlockChainIO interface.
+func (b *BtcWallet) GetCurrentHeight() (int32, error) {
+	_, height, err := b.rpc.GetBestBlock()
+	if err != nil {
+		return 0, err
+	}
+
+	return height, nil
+}
+
+// GetTxOut returns the original output referenced by the passed outpoint.
+//
+// This method is a part of the lnwallet.BlockChainIO interface.
+func (b *BtcWallet) GetUtxo(txid *wire.ShaHash, index uint32) (*wire.TxOut, error) {
+	txout, err := b.rpc.GetTxOut(txid, index, false)
+	if err != nil {
+		return nil, err
+	}
+
+	pkScript, err := hex.DecodeString(txout.ScriptPubKey.Hex)
+	if err != nil {
+		return nil, err
+	}
+
+	return &wire.TxOut{
+		// Sadly, gettxout returns the output value in BTC
+		// instead of satoshis.
+		Value:    int64(txout.Value) * 1e8,
+		PkScript: pkScript,
+	}, nil
+}
+
+// GetTransaction returns the full transaction identified by the passed
+// transaction ID.
+//
+// This method is a part of the lnwallet.BlockChainIO interface.
+func (b *BtcWallet) GetTransaction(txid *wire.ShaHash) (*wire.MsgTx, error) {
+	tx, err := b.rpc.GetRawTransaction(txid)
+	if err != nil {
+		return nil, err
+	}
+
+	return tx.MsgTx(), nil
+}