Evidence Source: NFC Reader

I've been working on software for an NFC reader off and on for a little over a year (https://github.com/bettse/janus) and the last time I was working on it, I began to realize that I was spending too much time trying to architect a platform for performing actions.  When I picked up the project again, I started by looking for an application that already handled the 'output' (actions), so that I might add the reader as an 'input' (EvidenceSource).  Although I'm not a regular user, I had played with ControlPlane in the past, so it came to mind.  I saw the USBEvidenceSource and took it as evidence that supporting this USB device would be possible.  I started porting my lower level device code into a plugin, and this PR is the result.

Since I'm not strongly familiar with the convention of the project, I'm guessing this will be far from in a state to actually merge.  I welcome any feedback that may get it closer to such a state.  I'm also aware that this also may be too esoteric to warrant inclusion in the mainline at all.

In terms of testing, this particular NFC reader is moderately difficult to acquire since the product line had been discontinued a year or two before company who produced it went out of business.  I have an extra that I can ship if there is interest.