Display lint overview in Diffusion

Summary: I will add links from /diffusion/ARC/lint/ in future diff.

Test Plan:
/diffusion/ - clicked on lint messages link.
/diffusion/ARC/ - clicked on lint messages link.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3926