PHUITimelineView

Summary:
Updates PhabricatorTimeline to PHUITimeline. Uses standard colors and spacing, softens up the actors, and reduces visual spacing of action-only events.

- Also updated some 2x sprite images.

Test Plan: Tested Tasks Paste and Pholio in my sandbox.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8205