…n FastJavaByteArrayYUVLuminanceSource and simplify CameraAnalyzer

Compared to existing ZXingSurfaceView, ZXingTextureView fixes the following:

- Ensure correct aspect ratio, no matter what the view size.
- Use background handler for all camera manipulation.
- Crop preview to match viewfinder, so that you only scan what you see.
- Avoid byte[] marshalling between Java and .Net runtime (FastJavaByteArray).
- Return buffer to java runtime with camera.AddCallbackBuffer.
- Avoid traslating from YCrCb to Rgb and back to luminance data (FastJavaByteArrayYUVLuminanceSource)
- Re-use buffers, to avoid memory pressure, when rotating.
- Automatically request autofocus on devices that does not support continous auto focus mode.
- Prefer continous mode
- For Xamarin.Forms ZXingScannerView now uses ZXingTextureView in the renderer on Android.

…d a FastJavaArrayEx.BlockCopyTo method to compensate for missing funtionality.

…ep a ringbuffer of recent barcodes, and honor DelayBetweenContinuousScans (of same barcode)