Allow to set a custom USB serial number

[szszszsz]

Allow user to set a custom USB serial number as a mean of personalization, or specifically naming the devices. This could be useful to determine, what device is connected in case of having multiple of them, and directly encoding the use case of such (work, home, etc.) in the USB serial number, which will show up in the PKCS#11 URL strings.

The custom-set serial number could be prefixed, to avoid collision with a real serial number, and avoid device spoofing (unless both devices are configured to do such).