Feature: NFC-tag as additional db key part

```
An NFC-tag (eg using a Samsung Nexus S) could be used instead of a keyfile (or 
the password) for a two-key verification or as an additional verification for a 
three-key verification.
```

Original issue reported on code.google.com by `masit...@gmail.com` on 22 Feb 2012 at 7:31
