Adding wikimetrics role and submodule

Wikimetrics is a Wikimedia Foundation developed tool that provides access to
the Wikimedia API. It allows users to pull data about a group of usernames
(called cohorts) to discover retention rates for those users, how many
characters they have added, how many edits they have made, how many pages they
have created, etc, all within time periods the Wikimetrics user sets.

Change-Id: Ie420012fe30899ca2e371323729241511a476d65