world_server: Enabled content_update (grass spreading)
N: content_update runs in its own thread
N: When your server closes, Clients get returned to the main menu
N: When clients disconnect, Server sees a simple message instead of an error
N: Other players see connects and disconnects in chat
Moved world_server_lock to world_server.server_lock so its more accessible
Disabled sending empty chat lines
Added some more thread locking