Fix EncodeQ implementation in PHPMailer, and provide SSL/TLS options

Summary:
See https://github.com/facebook/phabricator/commit/f5c2a2ab4bbe6317993fbcb406a86993e6ab75e0#commitcomment-2333247

Copy of working implementation from PHPMailerLite.

Also expose the SSL/TLS options.

Test Plan: Switched to this mailer, configured Gmail SMTP, sent email. Verified email arrived intact.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran, mbeck

Differential Revision: https://secure.phabricator.com/D4239