Add a way to deactivate mailman lists through the AlternC interface

[kienanstewart]

It would be nice to be able to deactivate/reactivate lists e-mails, in a manner similar to the other e-mails in AlternC. There are some possibilities to do it behind the scenes in mysql (eg. change the delivery), or by preventing mailman from reading the list information on disk; however, it would be quite convient to be able to have an operation available in the user interface to facilitate this.