[Redesign] Update Durable Column header
Summary: Shares more CSS between header styles, unifies the look. Ref T8099
Test Plan: Open and Close Durable Column a lot. Inspect pixels.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T8099
Differential Revision: https://secure.phabricator.com/D12877