Adds Tracker for Piwik

Extends the tracking API with a connector for Piwik. See
http://piwik.org/ for more information.

Change-Id: I60da59b0c1c06fc3bed4e1e99642bb275bee1ad0
Removes unused Google Analytics API

Change-Id: If9c9d1f9df0ae4ffc8c7f712f790b509988fbe49
Merge "Adds Tracker for Piwik"
Merge "Removes unused Google Analytics API"