Added service bell [MAP]

Added a service bell. The bell sits on various department desks throughout the station. When pressed, a sound will be played directly on all players in specified areas (For example, the cargo office and cargo bay back area). The areas are specified by editing the "departments" var in map editor and entering a list of area names to be affected. It has a 30 second cooldown, and the sound implemented currently is http://freesound.org/people/2887679652/sounds/171755/ (CC 0). The icon is the service bell already in our sprites.

Currently I've edited Box to have bells for the following areas:
*Cargo
*Security
*Bar and Kitchen
*Hydroponics
*Library
*RnD and Science hallway
*Robotics
*Medbay and chemistry

I've avoided having head's offices affected. It will only work when wrenched and in one of the areas specified. I was tempted to include something silly for emagging them, like 0 cooldown, an annoying buzz sound, or both, but as always I'm conscious about giving the emag yet more uses.

I haven't tinkered with machinery much before, so please point out any oversights or missing features/vars this should have.