Transactions - add "view raw" action

Summary: Use cutlery icon for hilarity. Ref T5768.

Test Plan: made something with remarkup in it, used 'view raw' and saw the remarkup raw in a nice little dialogue.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5768

Differential Revision: https://secure.phabricator.com/D10183