Set tabs corner widgets
        corner_widgets: dictionary of (corner, widgets)
        corner: Qt.TopLeftCorner or Qt.TopRightCorner
        widgets: list of widgets (may contains integers to add spacings)

def set_corner_widgets(self, corner_widgets):
        """
        Set tabs corner widgets
        corner_widgets: dictionary of (corner, widgets)
        corner: Qt.TopLeftCorner or Qt.TopRightCorner
        widgets: list of widgets (may contains integers to add spacings)
        """
        assert isinstance(corner_widgets, dict)
        assert all(key in (Qt.TopLeftCorner, Qt.TopRightCorner)
                   for key in corner_widgets)
        self.corner_widgets.update(corner_widgets)
        for corner, widgets in list(self.corner_widgets.items()):
            cwidget = QWidget()
            cwidget.hide()
            prev_widget = self.cornerWidget(corner)
            if prev_widget:
                prev_widget.close()
            self.setCornerWidget(cwidget, corner)
            clayout = QHBoxLayout()
            clayout.setContentsMargins(0, 0, 0, 0)
            for widget in widgets:
                if isinstance(widget, int):
                    clayout.addSpacing(widget)
                else:
                    clayout.addWidget(widget)
            cwidget.setLayout(clayout)
            cwidget.show()