'Clear/reset the widget.'

def clear(self):

    self.__data = None
    self.__pixmap = None
    self.__avgpixmap = None
    self.heatmap_item.setPixmap(QPixmap())
    self.averages_item.setPixmap(QPixmap())
    self.show_averages = True
    self.updateGeometry()
    self.layout().invalidate()
