Move rule change event into a rule observer and outside the Java api

* Move rule change event into a rule observer, without exposing it

* Fix comment

* Fix formatting changes added by my IDE

Still trying to configure it to force correctly the new style

Also remove some finals

src/main/java/carpet/script/CarpetEventServer.java

@@ -437,6 +437,11 @@ public class CarpetEventServer
             return events;
         }
 
+        static
+        {
+            Carpet.initCarpetEvents();
+        }
+
         public static final Event START = new Event("server_starts", 0, true)
         {
             @Override