Add a template to send welcome mails to New Members

[MaryOJob]

This is a feature request to see if we can add an email template that sends a welcome mail only to new members on a website.

[MaryOJob]

Even though we already send invoice paid mails, these would be sent every time a member checks out. In this case, we are looking at having one welcome email template sent only to new members signing up for the first time only.