Reduce reliance on getRevisionID() on DifferentialComment

Summary: Ref T2222. A few rendering interfaces rely on fishing the revision ID out of a DifferentialComment, but it will only have the PHID soon. Pass in the revision and use it to determine the ID instead.

Test Plan: Browsed, previewed, examined comments. Clicked anchors.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8209