implement cubes exporter for web viewer

engine/app_dialogs.cpp

@@ -258,6 +258,14 @@ void App::dialog_export()
     }
 }
 
+void App::dialog_export_cubes()
+{
+	if (canvas)
+	{
+		canvas->m_canvas->export_cubes(data_path + "/" + doc_name);
+	}
+}
+
 void App::dialog_layer_rename()
 {
     auto dialog = std::make_shared<NodeDialogLayerRename>();