Implements a World UID.

src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -395,10 +395,15 @@ public class CraftWorld implements World {
         return world.worldData.name;
     }
 
+    @Deprecated
     public long getId() {
         return world.worldData.getSeed();
     }
 
+    public long getUID() {
+        return world.worldData.getWorldUID();
+    }
+
     @Override
     public String toString() {
         return "CraftWorld{name=" + getName() + '}';