Add `qr_encode_wifi`

[jjcarstens]

Simple helper to format WiFi credentials with QR code formats which can be used on mobile devices to directly connect

[fhunleth]

This is really cool!

I have been concerned with the network requirement for generating QR codes and was looking into a simple QR code generator. I think it's not too hard if you put constraints on the inputs. Anyway, it doesn't look like the QR code requirements for WiFi credentials are too bad. Let me think about this a bit.

[fhunleth]

One other thought is to put the string generator in VintageNetWiFI (not the QR part). That way we keep it up to date with WiFi configs settings.