Improved detection of inaccurate system clock & nagging.

Now uses several NTP servers to determine mean offset from
system clock to internet time.

If abs(offset) > 500ms or NTP service not running then
user is 'nagged' via system tray pop-up notification
with instructions on how to fix.

Also improved system tray translations!

src/test/java/org/qora/test/NTPTests.java

@@ -0,0 +1,86 @@
+package org.qora.test;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.commons.net.ntp.NTPUDPClient;
+import org.apache.commons.net.ntp.NtpV3Packet;
+import org.apache.commons.net.ntp.TimeInfo;
+
+public class NTPTests {
+
+	private static final List<String> CC_TLDS = Arrays.asList("oceania", "europe", "lat", "asia", "africa");
+
+	public static void main(String[] args) throws UnknownHostException, IOException {
+		NTPUDPClient client = new NTPUDPClient();
+		client.setDefaultTimeout(2000);
+
+		System.out.println(String.format("%c%16s %16s %2s %c %4s %4s %3s %7s %7s %7s",
+				' ', "remote", "refid", "st", 't', "when", "poll", "reach", "delay", "offset", "jitter"
+		));
+
+		List<Double> offsets = new ArrayList<>();
+
+		List<String> ntpServers = new ArrayList<>();
+		for (String ccTld : CC_TLDS) {
+			ntpServers.add(ccTld + ".pool.ntp.org");
+			for (int subpool = 0; subpool <=3; ++subpool)
+				ntpServers.add(subpool + "." + ccTld + ".pool.ntp.org");
+		}
+
+		for (String server : ntpServers) {
+			try {
+				TimeInfo timeInfo = client.getTime(InetAddress.getByName(server));
+
+				timeInfo.computeDetails();
+				NtpV3Packet ntpMessage = timeInfo.getMessage();
+
+				System.out.println(String.format("%c%16.16s %16.16s %2d %c %4d %4d  %3o %6dms % 5dms % 5dms",
+						' ',
+						server,
+						ntpMessage.getReferenceIdString(),
+						ntpMessage.getStratum(),
+						'u',
+						0,
+						1 << ntpMessage.getPoll(),
+						1,
+						timeInfo.getDelay(),
+						timeInfo.getOffset(),
+						0
+				));
+
+				offsets.add((double) timeInfo.getOffset());
+			} catch (IOException e) {
+				// Try next server...
+			}
+		}
+
+		if (offsets.size() < ntpServers.size() / 2) {
+			System.err.println("Not enough replies");
+			System.exit(1);
+		}
+
+		double s0 = 0;
+		double s1 = 0;
+		double s2 = 0;
+
+		for (Double offset : offsets) {
+			// Exclude nearby results for more extreme testing
+			if (offset < 100.0)
+				continue;
+
+			s0 += 1;
+			s1 += offset;
+			s2 += offset * offset;
+		}
+
+		double mean = s1 / s0;
+		double stddev = Math.sqrt(((s0 * s2) - (s1 * s1)) / (s0 * (s0 - 1)));
+		System.out.println(String.format("mean: %7.3f, stddev: %7.3f", mean, stddev));
+	}
+
+}