R1:9f42bd791244

Based hovercards on ActionHeader

Summary: Refs T1048 - Makes it look //way// better

Test Plan: {F39347}

Reviewers: chad, epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1048

Differential Revision: https://secure.phabricator.com/D5587