Add Faction vaults.

These can be accessed with /f vault <number>
Set a Faction's max vaults with /f setmaxvaults <faction> <number> - can be run from console so Buycraft can execute it.
* This is a not very tested implementation. Should be tested more in depth before being pushed to a release.

src/main/java/com/massivecraft/factions/Conf.java

@@ -356,6 +356,9 @@ public class Conf {
     public static Set<String> worldsIgnorePvP = new LinkedHashSet<String>();
     public static Set<String> worldsNoWildernessProtection = new LinkedHashSet<String>();
 
+    // faction-<factionId>
+    public static String vaultPrefix = "faction-%s";
+
     public static Backend backEnd = Backend.JSON;
 
     public static transient int mapHeight = 8;