Add the given widget to the tooltip

        :param widget: the widget to add
        :type widget: QtGui.QWidget
        :returns: None
        :rtype: None
        :raises: None

def add_widget(self, widget):
        """Add the given widget to the tooltip

        :param widget: the widget to add
        :type widget: QtGui.QWidget
        :returns: None
        :rtype: None
        :raises: None
        """
        if self._buttons.get(widget):
            return
        btn = self.create_button(widget)
        cb = partial(self.focus_widget, w=widget)
        btn.clicked.connect(cb)
        self.layout().addWidget(btn)
        self._buttons[widget] = btn