Implement "ImageSource" (new tracker plugin) for libuvc

[rpavlik]

Follow on to #339 and pull #492, which did the hard work to map libuvc to an internal camera model and driver. Unfortunately while @toastedcrumpets was working on that, I was re-doing the hdk ir tracker plugin, including refactoring the internal camera interface, so that work only works on the "old and busted" plugin, not the "new hotness" plugin (which is better in pretty much every way).

Fortunately I don't think the port should be hard, since I did start with the code in the old plugin as I refactored the image capture. There's an initial attempt at #493 by @ChristophHaag (blobs-undo-bad was the branch name for the new tracker before it got merged to master) though he casts doubt on it in #492, so I'm not sure if it's up to date or usable, I haven't tested it.

[ChristophHaag]

I haven't tested for a while but it should still work fine.
I just mean I (or someone else) should probably look over it. For example b5ec8e8 is something that probably should not be in that pull request, it's just a quick fix for compiling osvr-core producing massive amounts of warnings so I didn't see warnings I cared about.
One thing I remember is that the new tracking code introduced a mandatory timestamp somewhere that might or might not be used correctly in my pull request. But as I said, the tracking always worked for me so it can't be too wrong.