Modernizing BarcodeScanner

[rlaurb]

There are a number of issues (mostly minor) with using BarcodeScanner with recent versions of Xcode, Swift, and iOS:
(1) Threading Issues: Every time I attempt to read a barcode, I get the following (backtrace omitted):
Thread Performance Checker: -[AVCaptureSession startRunning] should be called from background thread. Calling it on the main thread can lead to UI unresponsiveness
(2) There are a number of deprecations in the code, all easily solved:
(a) protocol definitions (protocol xxx: class {} instead of protocol xxx: AnyObject {})
(b) use of UIApplication.shared.statusBarOrientation
etc.