Have HTML mails return to and cc lines

Summary: Fixes T6525, adds cc and tos to html emails

Test Plan: send html and plain emails, see new stuff

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6525

Differential Revision: https://secure.phabricator.com/D10857