Add NFC Support

[CryptoGrampy]

• Should broadcast the monero payment URI via NFC
• Should use the web-nfc API (https://developer.mozilla.org/en-US/docs/Web/API/Web_NFC_API) (this api is experimental and HotShop NFC will likely only work on an Android device with Chromium at the moment)
• A Monerujo wallet should be able to tap the NFC and it should generate the same payment request as scanning the HotShop QR
• Can it work over Tor?

I have a possibly-working example here: https://github.com/CryptoGrampy/HotShop/tree/nfc that is deployed to hotshop-test.onrender.com . This needs to be tested with essentially 2 Android devices at the moment- one running HotShop and one running Monerujo (the only wallet that supports NFC). Additionally, the web-api does not work locally and has to be deployed to an https site.

[CryptoGrampy]

Requested NFC in Cake Wallet here: cake-tech/cake_wallet#376

[tidux]

Dumb question: would it be possible to extend this such that a "dumb" NFC hard-wallet could be implemented for Monero? No phone app required on the customer's end, just tap and PIN to pay like we get with fiat cards. As much as people like phone based NFC payment, there's still a massive market for standalone cards.

EDIT: Looks like this would be much easier with Seraphis.

[CryptoGrampy]

@tidux from everything i've heard, you basically must have an online device as a customer to be able to gather recent decoys to generate the transaction and this is not really something a vendor can do. I do think a simple tap to pay with a phone that looks something like, - merchant displays payment amount, user taps phone, request for XXX xmr pops up on phone with thumbprint or pin request to approve.