Added site retry to help reduce failed results due to timeouts

Waits 15 seconds before next try in case site is filtering too many
fast hits
Email notification improvements

- Added basic, initial layout for HTML-based email notification
- HTML email notification now includes the active listings HTML file
directly in the email

Note: Introduces bug where correct CSV is no longer attached.  Needs to
be fixed before release.
Fixed missing subject line in PHP-based emails