refs #419, reviewed style sheet paintEvent code

* removed for QWidget
* added for QDialog
http://stackoverflow.com/questions/37952348/enable-own-widget-for-stylesheet

src/blackgui/overlaymessages.h

@@ -113,9 +113,6 @@ namespace BlackGui
         //! \copydoc QFrame::keyPressEvent
         virtual void keyPressEvent(QKeyEvent *event) override;
 
-        //! \copydoc QFrame::paintEvent
-        virtual void paintEvent(QPaintEvent *event) override;
-
     private slots:
         //! Stylesheet changed
         void ps_onStyleSheetsChanged();