Listener optimizations (#1884)

* Drop CraftBukkit support, listeners cleanup

* Codestyle

* Codestyle

* Remove useless player.saveData() calls

* Micro optimization on the join process

* Requested changes

* Fix unit test

* Test onPlayerHeldItem listener

* Requested changes

* Remove unused import

src/main/java/fr/xephi/authme/message/MessageKey.java

@@ -146,6 +146,9 @@ public enum MessageKey {
     /** The server is full, try again later! */
     KICK_FULL_SERVER("on_join_validation.kick_full_server"),
 
+    /** An error occurred: unresolved player hostname! **/
+    KICK_UNRESOLVED_HOSTNAME("error.kick_unresolved_hostname"),
+
     /** Usage: /email add <email> <confirmEmail> */
     USAGE_ADD_EMAIL("email.usage_email_add"),