Fix #301 — Add global mail signature feature
Created by: ldidry
Add a etc/mail_tt2/message.global_footer
or etc/mail_tt2/message.global_footer.mime
file and it will be added to all messages.
Obviously, only admins can edit that file.
It can be used to add an unsubscribe link while letting users add their own list signature.
Will fix #301 (closed)