Track thank you emails to CiviMail

In make-thank-you, add CiviMail 'Mailing' records for each template.
Add mailing queue record for each message, use CiviMail VERP header for bounces.
Don't stop the show if we can't insert CiviMail records.

Change-Id: Id4f19ea94c1db82e838d7dd5439fb28a38c88a1a