mac: use native NSUserNotification (supported by qt) if possible
mac: use native NSUserNotification (supported by qt) if possible

wgaalves/seafile-client,haiwen/seafile-client,lucius-feng/seafile-client,losingle/seafile-client,daodaoliang/seafile-client,daodaoliang/seafile-client,losingle/seafile-client,wgaalves/seafile-client,lucius-feng/seafile-client,lucius-feng/seafile-client,daodaoliang/seafile-client,daodaoliang/seafile-client,wgaalves/seafile-client,haiwen/seafile-client,losingle/seafile-client,haiwen/seafile-client,lucius-feng/seafile-client,haiwen/seafile-client,wgaalves/seafile-client,losingle/seafile-client