List functionality

List functionality is provided by ForumListservProcessorMailet class. List functionality is currently:

• Adding of footer to mail messages
• Adding of subject prefix
• Providing a listname
• Setting of reply-to
• Setting headers for preventing looping: Set-X-Been-There

Future will be to extend list functionality by providing list server commands like:

• Subscribe
• Subscribe-confirm
• Unsubscribe
• Unsubscribe-confirm
• etc.