Add a "View Revision" button to HTML email
Ref T10694. If this feels good, I'd plan to eventually add something similar to other applications ("View Task", etc).
Not sure if we should keep the object link later in the mail body or not. I left it for now.
Reviewed By: epriestley
Maniphest Tasks: T10694
Differential Revision: https://secure.phabricator.com/D15884