Made the standard chair sprite a little bit wider to make buckling easier

Following https://tgstation13.org/phpBB/viewtopic.php?f=9&t=2273 about chair clicking,
I've recentered the sprite, made the chair two pixels wider in all orientations and the legs are one pixel wider as well. It's barely noticeable.

![](http://i62.tinypic.com/5s6e0.jpg)