PHPMailer SMTP - Plan for 2.2.0

Requirements for a 2.2.0 release

The alpha version supports formatting emails in HTML and adding attachments which removes the requirement of a separate module for formatting emails

It's more or less feature complete, but any bugs need to be ironed out before a full release.

• #3323476: Support adding attachments from the public file system →
• #3323669: Ignore format setting when not using PHPMailer SMTP as the formatter →
• #3324504: Nested multi-part content on second email sent by webform. →
• Use on multiple sites for a week and document any bugs
• Fix the bugs