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!

pom.xml

@@ -335,13 +335,12 @@
 			<artifactId>commons-text</artifactId>
 			<version>1.4</version>
 		</dependency>
-		<!-- No longer needed? Was used by NTP
+		<!-- For NTP -->
 		<dependency>
 			<groupId>commons-net</groupId>
 			<artifactId>commons-net</artifactId>
 			<version>3.3</version>
 		</dependency>
-		-->
 		<dependency>
 			<groupId>com.google.guava</groupId>
 			<artifactId>guava</artifactId>