Returns the very top window for all Qt purposes.
    
    :return     <QWidget> || None

def topWindow():
    """
    Returns the very top window for all Qt purposes.
    
    :return     <QWidget> || None
    """
    import_qt(globals())
    
    window = QtGui.QApplication.instance().activeWindow()
    if not window:
        return None
    
    parent = window.parent()
    
    while parent:
        window = parent
        parent = window.parent()
        
    return window