Make documentation items in user menu update as you navigate in Quicksand

Summary: Ref T5867. I sure love Javascript.

Test Plan: Navigated between Home, Diffusion and Differential, opening the user profile menu. Saw appropraite help items.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T5867

Differential Revision: https://secure.phabricator.com/D17214