Added an isStarted() method to Client.

jme3-networking/src/main/java/com/jme3/network/Client.java

@@ -55,6 +55,12 @@ public interface Client extends MessageConnection
      */
     public boolean isConnected();     
 
+    /**
+     *  Returns true if this client has been started and is still
+     *  running.
+     */
+    public boolean isStarted();
+
     /**
      *  Returns a unique ID for this client within the remote
      *  server or -1 if this client isn't fully connected to the