#758 Show login usage message on invalid arguments, #1053 send translatable "no permission" message

- Add default method to ExecutableCommand interface that allows to define the message key to show if a command's arguments are invalid. If not defined the behavior is as before: show the output of /<command> help
- Use translatable "no permission" message instead of hardcoded one

src/main/java/fr/xephi/authme/command/executable/changepassword/ChangePasswordCommand.java

@@ -49,4 +49,9 @@ public class ChangePasswordCommand extends PlayerCommand {
 
         management.performPasswordChange(player, oldPassword, newPassword);
     }
+
+    @Override
+    protected String getAlternativeCommand() {
+        return "/authme password <playername> <password>";
+    }
 }

src/main/java/fr/xephi/authme/command/executable/login/LoginCommand.java

@@ -1,6 +1,7 @@
 package fr.xephi.authme.command.executable.login;
 
 import fr.xephi.authme.command.PlayerCommand;
+import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.process.Management;
 import org.bukkit.entity.Player;
 
@@ -20,4 +21,14 @@ public class LoginCommand extends PlayerCommand {
         final String password = arguments.get(0);
         management.performLogin(player, password);
     }
+
+    @Override
+    public MessageKey getArgumentsMismatchMessage() {
+        return MessageKey.USAGE_LOGIN;
+    }
+
+    @Override
+    protected String getAlternativeCommand() {
+        return "/authme forcelogin <player>";
+    }
 }

src/main/java/fr/xephi/authme/command/executable/register/RegisterCommand.java

@@ -72,6 +72,11 @@ public class RegisterCommand extends PlayerCommand {
         return "/authme register <playername> <password>";
     }
 
+    @Override
+    public MessageKey getArgumentsMismatchMessage() {
+        return MessageKey.USAGE_LOGIN;
+    }
+
     private void handlePasswordRegistration(Player player, List<String> arguments) {
         if (isSecondArgValidForPasswordRegistration(player, arguments)) {
             final String password = arguments.get(0);