Places window in the center of the screen.

def place_center(window, width=None, height=None):
    """Places window in the center of the screen."""
    screenGeometry = QApplication.desktop().screenGeometry()

    w, h = window.width(), window.height()

    if width is not None or height is not None:
        w = width if width is not None else w
        h = height if height is not None else h
        window.setGeometry(0, 0, w, h)

    x = (screenGeometry.width() - w) / 2
    y = (screenGeometry.height() - h) / 2
    window.move(x, y)