[Redesign] Slight border inset on all profile photos

Summary: Ref T8099, Cleans up profile photos around the site in a more consistent way.

Test Plan: grep for 'background-size: 100%'

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13360