Implement wxListCtrl::GetEditControl() for wxQt

To get access to the control used for editing items, we need to create
it ourselves, which involves defining our own factory for doing this,
but seems to be the only way of achieving our goal.

Closes https://github.com/wxWidgets/wxWidgets/pull/1204

include/wx/qt/listctrl.h

@@ -10,7 +10,7 @@
 
 #include "wx/textctrl.h"
 
-class QTreeWidget;
+class wxQtTreeWidget;
 class QTreeWidgetItem;
 
 class WXDLLIMPEXP_FWD_CORE wxImageList;
@@ -303,7 +303,7 @@ protected:
                       m_ownsImageListSmall,
                       m_ownsImageListState;
 private:
-    QTreeWidget *m_qtTreeWidget;
+    wxQtTreeWidget *m_qtTreeWidget;
 
     wxDECLARE_DYNAMIC_CLASS( wxListCtrl );
 };