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/main/resources/i18n/SysTray_en.properties

@@ -1,14 +1,22 @@
 #Generated by ResourceBundle Editor (http://essiembre.github.io/eclipse-rbe/)
 # SysTray pop-up menu
 
+BLOCK_HEIGHT = height
+
 CHECK_TIME_ACCURACY = Check time accuracy
 
+CONNECTION = block
+
+CONNECTIONS = connections
+
 EXIT = Exit
 
 # Nagging about lack of NTP time sync
-NTP_NAG_CAPTION = No connections?
+NTP_NAG_CAPTION = Computer's clock is inaccurate!
 
-NTP_NAG_TEXT = Please enable Windows automatic time synchronization
+NTP_NAG_TEXT_UNIX = Install NTP service to get an accurate clock.
+
+NTP_NAG_TEXT_WINDOWS = Select "Synchronize clock" from menu to fix.
 
 OPEN_NODE_UI = Open Node UI
 

src/main/resources/i18n/SysTray_zh.properties

@@ -1,14 +1,20 @@
 #Generated by ResourceBundle Editor (http://essiembre.github.io/eclipse-rbe/)
 # SysTray pop-up menu
 
+BLOCK_HEIGHT = \u5757\u9AD8\u5EA6
+
 CHECK_TIME_ACCURACY = \u68C0\u67E5\u65F6\u95F4\u51C6\u786E\u6027
 
+CONNECTIONS = \u4E2A\u8FDE\u63A5
+
 EXIT = \u9000\u51FA\u8F6F\u4EF6
 
 # Nagging about lack of NTP time sync
-NTP_NAG_CAPTION = \u6CA1\u6709\u8FDE\u63A5\u4E0A\u8282\u70B9\uFF1F
+NTP_NAG_CAPTION = \u7535\u8111\u7684\u65F6\u949F\u4E0D\u51C6\u786E\uFF01
 
-NTP_NAG_TEXT = \u8BF7\u542F\u7528Windows\u81EA\u52A8\u65F6\u95F4\u540C\u6B65\u3002
+NTP_NAG_TEXT_UNIX = \u5B89\u88C5NTP\u670D\u52A1\u4EE5\u83B7\u5F97\u51C6\u786E\u7684\u65F6\u949F\u3002
+
+NTP_NAG_TEXT_WINDOWS = \u4ECE\u83DC\u5355\u4E2D\u9009\u62E9\u201C\u540C\u6B65\u65F6\u949F\u201D\u8FDB\u884C\u4FEE\u590D\u3002
 
 OPEN_NODE_UI = \u5F00\u542F\u754C\u9762