Merge the GO changes dfighter2->Master part 21

ADDED: GO_Button, GO_Door, and GO_Goober classes. These are mostly skeleton classes for now. However opening/closing should work just fine (when you open one of these, some of them have auto-close events, it should work just fine now ).

ADDED: GameObject::Open and GameObject::Close virtual methods. The names speak for themselves.
MODIFIED: Trap invisibility will now be set in GO_Trap::InitAI instead of the summon spell effect handler.