Update tasks/commits, remove diffs from Profile

Summary: Mostly a minor nit-pick, but I hate sending users off the profile and disorient them onto application search. These pages are pretty easy to maintain, I don't expect to need to do more here. I dropped Differential outright. Kept Tasks and Commits. Now you can browse everything about a user on their profile without leaving. Maybe add a link to ApplicationSearch? Not sure it's important.

Test Plan: Review tasks and commits on mine and other user profiles.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17470