Provide alternate, cropped photo for small displays

[aaronrudkin]

From @adamboche on May 27, 2017 23:54

Copied from original issue: voteview/WebVoteView#290

As per Alicia Parlapiano at the NYT, some images sometimes look rough when displayed small because the congressperson's face is too small relative to the overall picture canvas. We should, thus, provide alternate thumbnail versions in these cases which are cropped.

To do this, we would have to:

1. Use face detection to figure out what percentage of the frame the face takes up
2. If it is below a threshold, produce a cropped version
3. Identify images that should be thrown out because they give us nothing to work with.
4. Potentially offer a second set of photos altogether designed for small icon sized display.