Trigger change event for party create/disband (#4620)

src/main/java/com/gmail/nossr50/events/party/McMMOPartyChangeEvent.java

@@ -53,6 +53,16 @@ public class McMMOPartyChangeEvent extends PlayerEvent implements Cancellable {
      * A list of reasons why the event may have been fired
      */
     public enum EventReason {
+        /**
+         * Created a party.
+         */
+        CREATED_PARTY,
+
+        /**
+         * Disbanded a party.
+         */
+        DISBANDED_PARTY,
+
         /**
          * Joined a party for the first time.
          */