Messages should have their own index page. Currently if you visit
their URLs they acquire one from their ticket, with arbitrary results.
This would be the place to put options specififc to messages. Two
have already presented themselves, and the extra configuration
screen will prove useful as MailManager becomes more feature rich:
1. An export link for the message alone (not the whole ticket). This
functionality is already available, but only through the URL.
2. When we add the clamoured for facility to move individual
messages into different tickets its interface will naturally belong on a
message's index page.