Refactor Email class into separate classes

[jlbooker]

The Email class is a jumbled mess. We need to refactor it into separate classes.

• Each message in Email.php should have its own class.
• Use namespaces to create a sub-directory for all the messages. Something like: /class/EmailMessages/.php
• Create a parent class to avoid code duplication.
• Find and update all the places that make static class to Email:: to use the new message classes.
• Use the SwiftMailer API to send somewhat prettier HTML emails (use composer require to install SwiftMailer).

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