R1:46e5e79c4f08

Include custom header PHID in header logo cache key

Summary: Ref T4214. Reduce the need for installs to purge caches.

Test Plan:
{F329350}

- Changed header twice.
- New one showed up without dirtying cache.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4214

Differential Revision: https://secure.phabricator.com/D11965