Implement configurable currency formatting.

This commit enables users of different countries around the world to configure currency formatting displayed to users in a familiar manner.

Prior to this commit US formatting (symbols) was forced upon users. This is now configurable via locale values e.g. en-US, de, fr-ch.

This commit adds two new configurations:
- currency-format
- currency-symbol-format-locale

One method ISettings#getCurrencyFormat()

Essentials/src/com/earth2me/essentials/ISettings.java

@@ -8,6 +8,7 @@ import org.bukkit.configuration.ConfigurationSection;
 import org.bukkit.event.EventPriority;
 
 import java.math.BigDecimal;
+import java.text.NumberFormat;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -243,4 +244,6 @@ public interface ISettings extends IConf {
     boolean isSendFlyEnableOnJoin();
     
     boolean isWorldTimePermissions();
+    
+    NumberFormat getCurrencyFormat();
 }