Change appDelegate extension to extend UIViewController

[markmalone]

Currently the advice says one should add the following to the app delegate
extension UITableViewController {

    var appDelegate: AppDelegate { return (UIApplication.shared.delegate as! AppDelegate) }
   }

However changing it to

extension UIViewController {
    var appDelegate: AppDelegate { return (UIApplication.shared.delegate as! AppDelegate) }
   }

ensures it will work for any view controller subclass including a UIViewController that includes a table.