Enhance email headers and body

[w0rp]

The email headers for the price alerts aren't complete and may lead to the emails being bounced back as spam. The body of emails was put together very quickly and may also result in emails being bounced back as spam also, as small plain text emails are regrettably thought to be spam by many email providers. Dressing up emails with some simple HTML content would increase the likelihood of email delivery, which is a must-have for this project.