R1:1fc2dfd54baf

Load reviewer stats

Summary:
This allows getting stats for any arbitrary period, e.g.

- everything
- last week
- week before last week

Test Plan: Ran the script for last week.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3064