Conpherence - reply handler integration

Summary: Added a reply handler. A few problems -- first, I can't seem to get this to actually send me email so I haven't been able to reply (which I would have done by generating a reply, then copying the raw email into scripts/mail_handler.php). Second, the subject is often terrible on these emails -- unless the conpherence is named its something gross like "E4:" Third, on create I am noticing an error on array_combine() which I think is related to the need to write array_combine_not_broken or what have you I saw go by... (PhabricatorTransactionEditor does array_combine(xaction->getOldValue(), xaction->getOldValue()) and complains that the arrays are empty)

Test Plan: noted that /mail/ said mails were being sent

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T2399

Differential Revision: https://secure.phabricator.com/D4656