TitleBar: Move button construction into the FrameWorkWidgetFactory

So it can be more easily overridden by the user.
A virtual in TitleBarWidget is not good enough as we can't call virtuals
when in the ctor

src/private/widgets/TitleBarWidget_p.h

@@ -43,9 +43,6 @@ public:
     ///@brief getter for the close button
     QWidget* closeButton() const;
 
-    ///@brief
-    virtual QAbstractButton* createButton(QWidget *parent, TitleBarButtonType);
-
 protected:
     void paintEvent(QPaintEvent *) override;
     void mouseDoubleClickEvent(QMouseEvent *) override;
@@ -61,10 +58,7 @@ protected:
     bool isFloatButtonVisible() const override;
     bool isFloatButtonEnabled() const override;
 
-    QIcon iconForButtonType(TitleBarButtonType) const;
-
 private:
-    QString iconNameForButtonType(TitleBarButtonType) const;
     void init();
     int buttonAreaWidth() const;