Make Project Mobile menu more resilient

Summary: This sets $project at the controller level so it's available to building the icon nav and mobile menu, instead of guessing the $id. Fixes T7289

Test Plan: Test a project and its mobile menu when it does and does not have a workboard initialized. Also tested coming in via a slug and an id.

Reviewers: epriestley, btrahan

Reviewed By: btrahan

Subscribers: Korvin, epriestley

Maniphest Tasks: T7289

Differential Revision: https://secure.phabricator.com/D11848