Barsign sprites fix/update/whatever

Barsign sprites that have been sitting around since whenever `code/game/objects/effects/barsign.dm` stopped being #included. I've also added an "off" state to the .dmi, which is basically a non-animated version of the background image, without the icon that's present in the "empty" state:
![](http://puu.sh/ck4x5/69b6b8ff0d.png)

The "off" state is only pickable manually via ID swipe; it will not be randomly chosen for new barsigns.

Also removes the redundant file `code/game/objects/effects/barsign.dm`, since it's not #included, entirely unused, and is essentially a crappy, featureless version of `code/game/objects/structures/barsign.dm`.