Adds false bottom briefcases and an IAA traitor item.

As inspired by an anon in the general:
False bottom briefcases! Use a screwdriver to pop open a secret panel, which allows you to store an item that's invisible to a quick search. If you store a gun in the bottom, you can fire it by waving the briefcase angrily at another person.

The IAA gets a traitor item which is meant to be a useful assassination tool in the right hands: a false bottom briefcase with a starting SMG. Stealthy, but a pain to reload or put on burstfire since it's normally trapped in the briefcase. 6 TC, since it's a good weapon.
might want to do one of the ```put_in_hands``` procs so it goes in their off hand if it's free, and only pops out onto the floor if it's not