Allow AphrontDialogView to use PhabricatorActionHeaderView

Summary: We're baking some useful things into ActionHeader, would like to consolidate it's use around the site for consistency.

Test Plan: Tested log out dialog, attach dependencies, delete document in phriction.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin, AnhNhan

Differential Revision: https://secure.phabricator.com/D5635