og_mailinglist 6.x-1.0-beta8

Added integration with the Mailgun email service so now setting up and configuring a Mail Transfer Agent is not required.

As part of that, #911974: Send all emails through PHPMailer removing dependency on having a Sendmail compatible server was fixed.

IMPORTANT UPDATE NOTE:
You must now use our slightly forked version of the PHPMailer library found at https://github.com/KyleAMathews/phpmailer

There are a few variables such as the email's date that PHPMailer doesn't let us set that we fixed.

See https://github.com/KyleAMathews/phpmailer/commit/78cdf9743cc58f7e804207b... to see our changes.