Minor Robbery Features

Hello, first time contributor here! 

Having played this game for a couple of months, I thought I'd try my hand at contributing. The scope of this PR is intentionally very simple just to make sure I have a grasp on how the system works.

I added two features:

<b>ATMs can now be emagged.</b> They will shoot sparks, spew money, and lock the UI. Cash drop ranges randomly from $100 to $500. If someone has their ID in the ATM when it gets emagged, it will release the ID and not accept new IDs to prevent griefing.

<b>A new Cash Bag</b> which works like the Plant Bag but for space cash and coins to make robbing the ATMs a bit easier. The cash bag can be printed from the Botanist's Biogenerator for 400 pts, like a leather satchel.

These changes are intended to help admins run custom heist events.

I'm not much of an artist, but I tried to match the new Cash Bag with the existing style.
![Cash Bag Image](https://f.cloud.github.com/assets/2754163/1607291/8474c1cc-547b-11e3-9e95-269c2e7f6176.png)