Add support for gathering and displaying download statistics to our file hosting solution

[danilo, 2012-11-22] I am marking as Essential so we go through it in our planning call.
[asac, 2013-01-08] what details do you need?
[danilo, 2013-02-04] Asked Steve Taylor for details of how we should structure potential events, my original proposal is:

  Downloads :: Downloaded :: full-path-to-the-tar.bz2
  Downloads :: License Shown :: full-path-to-the-tar.bz2
  Downloads :: License Accepted :: full-path-to-the-tar.bz2
  Downloads :: License Rejected :: full-path-to-the-tar.bz2
  Downloads :: OpenID Requested :: full-path-to-the-tar.bz2
  Downloads :: OpenID Success :: full-path-to-the-tar.bz2
  Downloads :: OpenID Failed :: full-path-to-the-tar.bz2
[danilo, 2013-02-04] Adding events to GA should be simple: _gaq.push(['_trackEvent', 'Downloads', 'Downloaded', '/android/blah/blah/foo.tar.bz2']);
[danilo, 2013-03-01] Verified to work for releases.linaro.org: snapshots.linaro.org was never set up for tracking it seems. Still need to gather feedback from Steve Taylor, but I'll do that at Connect.

Meta:
Headline: Enable tracking of downloads in Google Analytics for snapshots.linaro.org and releases.linaro.org.
Acceptance: Downloads start showing up in Google Analytics.
Roadmap id: NA

Work items:
[danilo] Ask about what should we do to label downloads for google analytics event tracking: POSTPONED
Implement using Google Analytics Event Tracking: DONE
Verify it works for all the events we are supposed to record: DONE