Automatic turn off in advanced mode

[bramborman]

I'm not sure how other people use this app, but my usage pattern is usually turn NFC on, pay, turn NFC off. I turn the NFC off almost immediately after the payment, if I don't forget 😅
It would be really helpful if I could select a time after which it would be automatically turned off after turning it on. That way I wouldn't have to worry about turning it off myself and would be free of the threat of forgetting 😁
This would, of course, be possible only with the advanced mode and ideally be configurable in a popup (#49).