Include added reviewers and ccs in preview

Summary: Preview of Add Reviewers looks silly without actually showing them

Test Plan:
Go to any diff
Leap into action: Add Reviewers
Add some reviewers
Write some comment
Preview including Added reviewers should be displayed
Change action to Comment
Added reviewers should disappear
Repeat with Add CCs

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley, vrana

Differential Revision: https://secure.phabricator.com/D1276