[Enhancement] - Added boolean value to enable or disable greeting, ungreeting and trade npc callback

[dudantas]

This will allow us to control which npcs will have, by default, the greet, ungreet and trade callbacks enabled, if false, the npc will not use the callback and will need to use something custom If no parameter (true or false) is provided in the npc NpcHandler:addModule, it will inform the distro with a warning and set the default to true

Added to disable trade callback on "Yana, Peter and Sandomo" npcs (and allow the possibility of modifying in other npcs if necessary)