Initial Litecoin support

Added altcoinj library as Maven dependency.

Added new Litecoin subclass of Bitcoiny,
with mainnet and testnet ElectrumX server lists.

Added litecoinNet settings variable and getter.

Added LitecoinTests.
Most tests work but testFindHtclSecret()
needs a redeemed HTLC on chain (not yet done).

Added litecoinNet to some test settings files
in resources.

Added Litecoin BuildHTLC, Refund test apps.

Added SendLTC app as Electrum-LTC seems a bit flaky?

So far managed to build HTLC P2SH, fund it and then
refund it!

---

As Bitcoin and Litecoin are both subclasses of Bitcoiny,
could unify some test apps with added Bitcoin/Litecoin
switch as first arg?

src/main/java/org/qortal/crosschain/Litecoin.java

@@ -0,0 +1,166 @@
+package org.qortal.crosschain;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.EnumMap;
+import java.util.Map;
+
+import org.bitcoinj.core.Context;
+import org.bitcoinj.core.NetworkParameters;
+import org.libdohj.params.LitecoinMainNetParams;
+import org.libdohj.params.LitecoinRegTestParams;
+import org.libdohj.params.LitecoinTestNet3Params;
+import org.qortal.crosschain.ElectrumX.Server;
+import org.qortal.crosschain.ElectrumX.Server.ConnectionType;
+import org.qortal.settings.Settings;
+
+public class Litecoin extends Bitcoiny {
+
+	public static final String CURRENCY_CODE = "LTC";
+
+	// Temporary values until a dynamic fee system is written.
+	private static final long MAINNET_FEE = 1000L;
+	private static final long NON_MAINNET_FEE = 1000L; // enough for TESTNET3 and should be OK for REGTEST
+
+	private static final Map<ElectrumX.Server.ConnectionType, Integer> DEFAULT_ELECTRUMX_PORTS = new EnumMap<>(ElectrumX.Server.ConnectionType.class);
+	static {
+		DEFAULT_ELECTRUMX_PORTS.put(ConnectionType.TCP, 50001);
+		DEFAULT_ELECTRUMX_PORTS.put(ConnectionType.SSL, 50002);
+	}
+
+	public enum LitecoinNet {
+		MAIN {
+			@Override
+			public NetworkParameters getParams() {
+				return LitecoinMainNetParams.get();
+			}
+
+			@Override
+			public Collection<ElectrumX.Server> getServers() {
+				return Arrays.asList(
+						// Servers chosen on NO BASIS WHATSOEVER from various sources!
+						new Server("electrum-ltc.someguy123.net", Server.ConnectionType.SSL, 50002),
+						new Server("backup.electrum-ltc.org", Server.ConnectionType.TCP, 50001),
+						new Server("backup.electrum-ltc.org", Server.ConnectionType.SSL, 443),
+						new Server("electrum.ltc.xurious.com", Server.ConnectionType.TCP, 50001),
+						new Server("electrum.ltc.xurious.com", Server.ConnectionType.SSL, 50002),
+						new Server("electrum-ltc.bysh.me", Server.ConnectionType.SSL, 50002),
+						new Server("ltc.rentonisk.com", Server.ConnectionType.TCP, 50001),
+						new Server("ltc.rentonisk.com", Server.ConnectionType.SSL, 50002),
+						new Server("electrum-ltc.petrkr.net", Server.ConnectionType.SSL, 60002),
+						new Server("ltc.litepay.ch", Server.ConnectionType.SSL, 50022));
+			}
+
+			@Override
+			public String getGenesisHash() {
+				return "12a765e31ffd4059bada1e25190f6e98c99d9714d334efa41a195a7e7e04bfe2";
+			}
+
+			@Override
+			public long getP2shFee(Long timestamp) {
+				// TODO: This will need to be replaced with something better in the near future!
+				return MAINNET_FEE;
+			}
+		},
+		TEST3 {
+			@Override
+			public NetworkParameters getParams() {
+				return LitecoinTestNet3Params.get();
+			}
+
+			@Override
+			public Collection<ElectrumX.Server> getServers() {
+				return Arrays.asList(
+						new Server("electrum-ltc.bysh.me", Server.ConnectionType.TCP, 51001),
+						new Server("electrum-ltc.bysh.me", Server.ConnectionType.SSL, 51002),
+						new Server("electrum.ltc.xurious.com", Server.ConnectionType.TCP, 51001),
+						new Server("electrum.ltc.xurious.com", Server.ConnectionType.SSL, 51002));
+			}
+
+			@Override
+			public String getGenesisHash() {
+				return "4966625a4b2851d9fdee139e56211a0d88575f59ed816ff5e6a63deb4e3e29a0";
+			}
+
+			@Override
+			public long getP2shFee(Long timestamp) {
+				return NON_MAINNET_FEE;
+			}
+		},
+		REGTEST {
+			@Override
+			public NetworkParameters getParams() {
+				return LitecoinRegTestParams.get();
+			}
+
+			@Override
+			public Collection<ElectrumX.Server> getServers() {
+				return Arrays.asList(
+						new Server("localhost", Server.ConnectionType.TCP, 50001),
+						new Server("localhost", Server.ConnectionType.SSL, 50002));
+			}
+
+			@Override
+			public String getGenesisHash() {
+				// This is unique to each regtest instance
+				return null;
+			}
+
+			@Override
+			public long getP2shFee(Long timestamp) {
+				return NON_MAINNET_FEE;
+			}
+		};
+
+		public abstract NetworkParameters getParams();
+		public abstract Collection<ElectrumX.Server> getServers();
+		public abstract String getGenesisHash();
+		public abstract long getP2shFee(Long timestamp) throws ForeignBlockchainException;
+	}
+
+	private static Litecoin instance;
+
+	private final LitecoinNet litecoinNet;
+
+	// Constructors and instance
+
+	private Litecoin(LitecoinNet litecoinNet, BitcoinyBlockchainProvider blockchain, Context bitcoinjContext, String currencyCode) {
+		super(blockchain, bitcoinjContext, currencyCode);
+		this.litecoinNet = litecoinNet;
+
+		LOGGER.info(() -> String.format("Starting Litecoin support using %s", this.litecoinNet.name()));
+	}
+
+	public static synchronized Litecoin getInstance() {
+		if (instance == null) {
+			LitecoinNet litecoinNet = Settings.getInstance().getLitecoinNet();
+
+			BitcoinyBlockchainProvider electrumX = new ElectrumX(litecoinNet.getGenesisHash(), litecoinNet.getServers(), DEFAULT_ELECTRUMX_PORTS);
+			Context bitcoinjContext = new Context(litecoinNet.getParams());
+
+			instance = new Litecoin(litecoinNet, electrumX, bitcoinjContext, CURRENCY_CODE);
+		}
+
+		return instance;
+	}
+
+	// Getters & setters
+
+	public static synchronized void resetForTesting() {
+		instance = null;
+	}
+
+	// Actual useful methods for use by other classes
+
+	/**
+	 * Returns estimated LTC fee, in sats per 1000bytes, optionally for historic timestamp.
+	 * 
+	 * @param timestamp optional milliseconds since epoch, or null for 'now'
+	 * @return sats per 1000bytes, or throws ForeignBlockchainException if something went wrong
+	 */
+	@Override
+	public long getP2shFee(Long timestamp) throws ForeignBlockchainException {
+		return this.litecoinNet.getP2shFee(timestamp);
+	}
+
+}

src/main/java/org/qortal/settings/Settings.java

@@ -21,6 +21,7 @@ import org.eclipse.persistence.jaxb.JAXBContextFactory;
 import org.eclipse.persistence.jaxb.UnmarshallerProperties;
 import org.qortal.block.BlockChain;
 import org.qortal.crosschain.Bitcoin.BitcoinNet;
+import org.qortal.crosschain.Litecoin.LitecoinNet;
 
 // All properties to be converted to JSON via JAXB
 @XmlAccessorType(XmlAccessType.FIELD)
@@ -98,6 +99,7 @@ public class Settings {
 	// Which blockchains this node is running
 	private String blockchainConfig = null; // use default from resources
 	private BitcoinNet bitcoinNet = BitcoinNet.MAIN;
+	private LitecoinNet litecoinNet = LitecoinNet.MAIN;
 	// Also crosschain-related:
 	/** Whether to show SysTray pop-up notifications when trade-bot entries change state */
 	private boolean tradebotSystrayEnabled = false;
@@ -370,6 +372,10 @@ public class Settings {
 		return this.bitcoinNet;
 	}
 
+	public LitecoinNet getLitecoinNet() {
+		return this.litecoinNet;
+	}
+
 	public boolean isTradebotSystrayEnabled() {
 		return this.tradebotSystrayEnabled;
 	}