Make it possible for the available scene types to be easily augmented.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3505 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/stage/tools/editor/EditorApp.java

@@ -238,6 +238,15 @@ public class EditorApp implements Runnable
         return new EditorFrame();
     }
 
+    /**
+     * Derived classes can override this method and add additional scene
+     * types.
+     */
+    protected void enumerateSceneTypes (List types)
+    {
+        types.add(StageSceneModel.WORLD);
+    }
+
     /**
      * Instantiate the application object and start it running.
      */
@@ -322,7 +331,7 @@ public class EditorApp implements Runnable
 	}
 
         public void enumerateSceneTypes (List types) {
-            types.add(StageSceneModel.WORLD);
+            EditorApp.this.enumerateSceneTypes(types);
         }
     }