new relic s3 plugin

@e0d 

Still a work in progress but if you have time, it may be worthwhile to review.

Big TODO's at this writing:
* daemonize it via supervisor (I'm going to do that last, potentially in a separate PR)
* I was not using common because of everything that comes with it. Rbenv does not have an explicit dependency on common; however, it is unable to function without it because it needs to use git. So I'm either going to establish a dependency on common, or solve it some other way.
Is the plan to move this under the edx org?