Use PhabricatorEdgeType strings when rendering transactions

Summary:
Ref T5245. This hooks up the translation/rendering methods added previously.

These are messy, but now extractable/translatable.

Test Plan: Viewed edge transactions and stories, saw correct strings.

Reviewers: chad, btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5245

Differential Revision: https://secure.phabricator.com/D9841