Refactored method naming

Changed NPC#getUUID to more appropriate NPC#getUniqueId

api/src/main/java/net/jitse/npclib/internal/NPCBase.java

@@ -62,7 +62,7 @@ public abstract class NPCBase implements NPC, NPCPacketHandler {
         return instance;
     }
     
-    public UUID getUUID() {
+    public UUID getUniqueId() {
         return uuid;
     }