Email template enhancements

[goldpbear]

Thanks to @zmbc we have a place email template feature on the API that allows us to automatically send emails when new content is created on a Mapseed map.

This works great, but a recent use case suggested some useful enhancements:

• Send email on comment submissions -- Support notification emails for comments, etc. #124
• The option to list multiple emails in the BCC field -- Multiple emails in place email template BCC list #121
• Send email to the BCC list even if the no submitter email is provided -- Consistently send email to place email template BCC list #122