Gui: [skip ci] fix -Wodr

The forward declarations of QuantitySpinBox and Ui_TaskAppearance were done in the wrong namespace

src/Gui/TaskCSysDragger.h

@@ -26,10 +26,9 @@
 #include <Gui/TaskView/TaskDialog.h>
 #include <App/DocumentObserver.h>
 
-class QuantitySpinBox;
-
 namespace Gui
 {
+  class QuantitySpinBox;
   class SoFCCSysDragger;
   class ViewProviderDragger;
   

src/Gui/TaskView/TaskAppearance.h

@@ -29,16 +29,17 @@
 #include <boost/signals2.hpp>
 
 
-class Ui_TaskAppearance;
-
 namespace App {
 class Property;
 }
 
 namespace Gui {
 class ViewProvider;
+
 namespace TaskView {
+
 typedef boost::signals2::connection TaskAppearance_Connection;
+class Ui_TaskAppearance;
 
 class TaskAppearance : public TaskBox, public Gui::SelectionSingleton::ObserverType
 {