Allow MetaMTAMail to send with a raw "From" address

Summary:
Ref T7607. Ref T7522.

• For the import tools, I want to send from "Phacility Support <support@phacility.com>".
• In the general case, I want to send billing mail from merchants (T7607) later on.

Test Plan: Sent an email and saw the desired "From" address.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7607, T7522

Differential Revision: https://secure.phabricator.com/D12100