Add support for NFC

[msirringhaus]

First shot at supporting NFC.

• Switched to my libwebauthn fork for now, until it lands (so this PR can be considered a draft)
• nfc.rs is more or less a direct copy of usb.rs with the removal of "selecting device" which as of now isn't a thing in the NFC-implementation of libwebauthn. They probably could also share most/all of the code, but I'm not sure yet if we would want that.
• I also had the GUI-side duplicated, but de-duplicated it later on. Not sure which way we want to go there. Both are there in the history, so easily just one or the other
• Changed the icon to the not-really-fitting wifi-symbol, as I couldn't find any nfc-icons in the common themes.
• get_available_public_key_devices() is not using a static list anymore but dynamically checks on each call if NFC is available (because someone may plug in their NFC reader and try again).
• No additional tests for now

[AlfioEmanueleFresta]

LGTM!