Implemented the unregister command

src/main/java/fr/xephi/authme/command/executable/unregister/UnregisterCommand.java

@@ -0,0 +1,52 @@
+package fr.xephi.authme.command.executable.unregister;
+
+import fr.xephi.authme.AuthMe;
+import fr.xephi.authme.cache.auth.PlayerCache;
+import fr.xephi.authme.command.CommandParts;
+import fr.xephi.authme.command.ExecutableCommand;
+import fr.xephi.authme.settings.Messages;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+
+public class UnregisterCommand extends ExecutableCommand {
+
+    /**
+     * Execute the command.
+     *
+     * @param sender The command sender.
+     * @param commandReference The command reference.
+     * @param commandArguments The command arguments.
+     *
+     * @return True if the command was executed successfully, false otherwise.
+     */
+    @Override
+    public boolean executeCommand(CommandSender sender, CommandParts commandReference, CommandParts commandArguments) {
+        // AuthMe plugin instance
+        final AuthMe plugin = AuthMe.getInstance();
+
+        // Messages instance
+        final Messages m = Messages.getInstance();
+
+        // Make sure the current command executor is a player
+        if(!(sender instanceof Player)) {
+            return true;
+        }
+
+        // Get the password
+        String playerPass = commandArguments.get(0);
+
+        // Get the player instance and name
+        final Player player = (Player) sender;
+        final String playerNameLowerCase = player.getName().toLowerCase();
+
+        // Make sure the player is authenticated
+        if (!PlayerCache.getInstance().isAuthenticated(playerNameLowerCase)) {
+            m.send(player, "not_logged_in");
+            return true;
+        }
+
+        // Unregister the player
+        plugin.management.performUnregister(player, playerPass, false);
+        return true;
+    }
+}