R1:7c5f71b6914c

Subclass most ReplyHandlers from TransactionReplyHandler

Summary: Ref T7199. Half of these aren't even reachable, but make some progress toward reducing the amount of nonsense and garbage in mail handling.

Test Plan: Tested all reachable handlers with `bin/mail receive-test`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7199

Differential Revision: https://secure.phabricator.com/D12237