added a new 'ShutdownMessage' for the server

Projekte/mdga/model/src/main/java/pp/mdga/message/server/ShutdownMessage.java

@@ -0,0 +1,30 @@
+package pp.mdga.message.server;
+
+import com.jme3.network.serializing.Serializable;
+
+/**
+ * A message sent by the server to inform the clients that the server is shutting down.
+ */
+@Serializable
+public class ShutdownMessage extends ServerMessage {
+    /**
+     * Accepts a visitor to process this message.
+     *
+     * @param interpreter the visitor to process this message
+     */
+    @Override
+    public void accept(ServerInterpreter interpreter) {
+        interpreter.received(this);
+    }
+
+    /**
+     * Gets the bundle key of the informational text to be shown at the client.
+     * This key is used to retrieve the appropriate localized text for display.
+     *
+     * @return the bundle key of the informational text
+     */
+    @Override
+    public String getInfoTextKey() {
+        return "";
+    }
+}