[OzzModz] Private Threads for XenForo 2.1.0 Beta 2

Private threads allows users to create threads that can't be viewed by members unless they have been invited to view the thread.

FEATURES:

• Prepend/Append text to thread titles
• Change existing threads to private threads
• Change private threads to public threads
• Alert members when they are included in a private thread
• Add/Remove members after the thread is created

NOTE: For security reasons admins can view all private threads. Moderators can not. Only the original thread starter can make a thread private/public.