Migrated QRChestra to unified API

- Added NSTimer parameter declatation to method to be used as
Action<NSTimer>
- AVCaptureMode.ModeAutoFocus to .AutoFocus (removed Mode from beginning
of other values in enum)
- AVCaptureVideoPreviewLayer.LayerVideoGravity to .VideoGravity
- Changed NSString.DataUsingEncoding to .Encode
- Removed (NSTimer>) cast from NSTimer.CreateScheduledTimer(double,
NSObject, Selector, NSObject, bool)
- Removed (NSTimer>) cast from
NSTimer.CreateRepeatingScheduledTimer(double, Action<NSTimer>)