Move chair buckling behaviour to /obj/stool

[babayetu83]

I kinda just see stools as less secure than chairs, since there's no back support. Nothing to keep you propped up.

Would be neat to have more things you can do with them though, like how you can fold up and pick up chairs.

just say the backs of them are invisible. space age future megastools. or alternatively, the buckle could be around the waist like a seatbelt designed to keep the occupant seated