Enable NFC push message

Given we have the nice icon from carrie, and the screen is there ready to go, it should allow people to use NFC to swap. I believe it is relatively straight forward. That is, tell the NFC adapter to register the swap URI as the data it wants to "beam" (or whatever term they want to use).

As a side note, I wonder what should happen if you don't have NFC enabled? Maybe a status on the screen, and a button saying "Touch to enable NFC" like the WiFi screen?

Status changed to closed

Turns out I had already set this up, but not exactly correctly. It would only do so if the user hadn't previously disabled the "Touch devices together" screen during an earlier swap. Now it should always be enabled, even if that screen is skipped.