iOS8中想要一次性设置 status 隐藏, 需要在 info.plist 文件中加入一个
View controller-based status bar appearance
并设置为 NO, 这是告诉系统status bar不依赖于UIViewController. 这样就可以通过
application.statusBarHidden = YES;
View controller-based status bar appearance
application.statusBarHidden = YES;