swift activity indicator
//https://medium.com/swlh/how-to-give-your-viewcontroller-an-activity-indicator-4c3bfd84893e
//Controller Class
var activityIndicator = UIActivityIndicatorView(style: .Large)
//inside ViewDidLoad
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(activityIndicator)
activityIndicator.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
activityIndicator.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
//now use anywhere to start and stop animation
activityIndicator.startAnimating()
//and
activityIndicator.stopAnimating()