Integrate AWS Image Recognition (Rekognition)

[jeffpaul]

Splitting this out from #28, via @ryanwelcher:

I have some experience working with AWS using the Image Recognition ( Rekognition ) tool so that may be a good place to start if/when we decide to add another provider.

[jeffpaul]

Will want to ensure this includes UI for filtering in the Media Library (currently in backbone.js).