Add the error acceptance median as a settable attribute in barcodescanner

Current barcodescanner implementation uses a median error value acceptance based on the following post:
https://github.com/serratus/quaggaJS/issues/237#issuecomment-389667599

https://github.com/zkoss/zkcml/blob/master/zkmax/src/archive/web/js/zkmax/barscanner/Barcodescanner.js#L559-L564

At the moment, the acceptance value is hardcoded at 0.1, and is defined in a library initialization object, which is not easy to override without replacing the whole init function.

It would be good to use a widget value (with component getter / setter / attribute in zul) to give developers the option to turn this feature off (set to 1) or require a stricter or looser safety check.