Email utilities for Moodle

This plugin is intended to become a place for a suite of semi related email utilities
to help improve the security, scalability, and performance of emails.

A rough roadmap with no set timelines:

* Handle incoming email complaints via AWS SES Complaints
* Email round trip monitoring, eg sends an email to itself and asserts it arrives and in the right shape
* DMARC email processing and reporting

DKIM Manager

In the admin settings there is a new admin page for creating and managing DKIM
certificate pairs, showing the DNS records, validating, activating and testing them.

Admin > Server > Email > DKIM manager

AWS SES Complaints Plugin for Moodle

This plugin is for use with the AWS SES service.

The complaints list (/admin/tool/emailutils/index.php) is not implemented yet.