Extract datadog reporting from accumulator.

[bradylove]

Once #3 is merged, it would be nice to move the datadog reporting to its own application so that people who wish to use the noisy neighbor nozzle but do not wish to use datadog are still able to do so.

It would also be nice to re-structure the datadog reporter to have some sort of client for the accumulator that others can use to to build their own reporters.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/153582610

The labels on this github issue will be updated when the story is started.