[MAKEAPI] Fix Bug 910403: Create endpoint for delivering metrics from MakeAPI (for services like GeckoBoard)

Hi,

All endpoints are functioning correct. If you would like to test this you can use the following endpoints:

  /metrics/makes/all
  /metrics/makes/day
  /metrics/makes/week
  /metrics/remixes/all
  /metrics/remixes/day
  /metrics/remixes/week

> Initially, we can set up a page that displays the metrics to logged in administrators. 
> use the admin console as a model. `/admin/metrics` sounds like a nice place to put it. 
> In the future we could protect the metrics routes with Hawk and allow authenticated calls to it by admin keys.

Note: I'm finished with the backend code. I would like to make a pull request and submit my code to Mozilla. 

I'd like to ask Cade a few questions about the UI as well as admin keys. Perhaps we could create a new bug for the UI for the metrics & Hawk Authentication.