Receive to and send from native segwit addresses

- Hierarchical-deterministic derivation of native segwit addresses.
- Receive payments to native segwit addresses.
- Spend and sign payments from native segwit addresses.
- Watch-only wallets with native segwit addresses (zpub/vpub).
- WalletAppKit, Wallet-tool and Wallet-template are taught to deal with segwit-enabled wallets.

Be aware this adds a new field in the wallet protobuf: output_script_type in Key, which keeps track
of the script type of DeterministicKeyChains. Protobufs will be migrated; old DeterministicKeyChains
are assumed to be of type P2PKH.

Includes some code by Fabrice Drouin.

wallettemplate/src/main/java/wallettemplate/Main.java

@@ -22,6 +22,7 @@ import org.bitcoinj.core.NetworkParameters;
 import org.bitcoinj.core.Utils;
 import org.bitcoinj.kits.WalletAppKit;
 import org.bitcoinj.params.*;
+import org.bitcoinj.script.Script;
 import org.bitcoinj.utils.BriefLogFormatter;
 import org.bitcoinj.utils.Threading;
 import org.bitcoinj.wallet.DeterministicSeed;
@@ -46,6 +47,7 @@ import static wallettemplate.utils.GuiUtils.*;
 
 public class Main extends Application {
     public static NetworkParameters params = MainNetParams.get();
+    public static final Script.ScriptType PREFERRED_OUTPUT_SCRIPT_TYPE = Script.ScriptType.P2WPKH;
     public static final String APP_NAME = "WalletTemplate";
     private static final String WALLET_FILE_NAME = APP_NAME.replaceAll("[^a-zA-Z0-9.-]", "_") + "-"
             + params.getPaymentProtocolId();
@@ -132,7 +134,7 @@ public class Main extends Application {
 
     public void setupWalletKit(@Nullable DeterministicSeed seed) {
         // If seed is non-null it means we are restoring from backup.
-        bitcoin = new WalletAppKit(params, new File("."), WALLET_FILE_NAME) {
+        bitcoin = new WalletAppKit(params, PREFERRED_OUTPUT_SCRIPT_TYPE, null, new File("."), WALLET_FILE_NAME) {
             @Override
             protected void onSetupCompleted() {
                 // Don't make the user wait for confirmations for now, as the intention is they're sending it

wallettemplate/src/main/java/wallettemplate/SendMoneyController.java

@@ -58,6 +58,7 @@ public class SendMoneyController {
         new TextFieldValidator(amountEdit, text ->
                 !WTUtils.didThrow(() -> checkState(Coin.parseCoin(text).compareTo(balance) <= 0)));
         amountEdit.setText(balance.toPlainString());
+        address.setPromptText(Address.fromKey(Main.params, new ECKey(), Main.PREFERRED_OUTPUT_SCRIPT_TYPE).toString());
     }
 
     public void cancel(ActionEvent event) {

wallettemplate/src/main/resources/wallettemplate/send_money.fxml

@@ -33,7 +33,7 @@
                         <Font size="24.0" />
                      </font>
                   </Label>
-              <TextField fx:id="address" maxWidth="1.7976931348623157E308" promptText="1EZEqFBd8yuc9ir2761987q7k3VcALC8YQ" HBox.hgrow="ALWAYS">
+              <TextField fx:id="address" maxWidth="1.7976931348623157E308" HBox.hgrow="ALWAYS">
                 <VBox.margin>
                   <Insets />
                 </VBox.margin>