Add very very basic reporting to Maniphest

Summary: Rough cut for Quora, we want this too eventually but it's super basic
right now so I'm not linking it anywhere. Once we get a couple more iterations
I'll put it in the UI.

Test Plan: Looked at stats for test data.

Reviewers: btrahan

Reviewed By: btrahan

CC: anjali, aran, epriestley

Differential Revision: https://secure.phabricator.com/D1594