quick fix sdk now use LegacyApplication according to the last version 3.1.0-alpha4

jme3-core/src/com/jme3/gde/core/scene/SceneApplication.java

@@ -24,7 +24,7 @@
  */
 package com.jme3.gde.core.scene;
 
-import com.jme3.app.Application;
+import com.jme3.app.LegacyApplication;
 import com.jme3.app.StatsView;
 import com.jme3.asset.AssetManager;
 import com.jme3.bullet.BulletAppState;
@@ -86,7 +86,7 @@ import org.openide.util.lookup.Lookups;
  * @author normenhansen
  */
 @SuppressWarnings({"unchecked", "rawtypes"})
-public class SceneApplication extends Application implements LookupProvider {
+public class SceneApplication extends LegacyApplication implements LookupProvider {
 
     private static final Logger logger = Logger.getLogger(SceneApplication.class.getName());
     private static boolean failMessageShown = false;