emag refactor

moves emag effects from attackby() into atom proc emag_act()

this affects the following:
supply computer
bots
clone pods
holodeck computer
arcade
comm console
message monitor
emergency shuttle computer
sec barrier
door control
door
windoor
portaturret
portaturret switch
crusher
shield generator
slot machine
telecomm computers
old turret switch
vending machine
mech fab
light replacer
defib
lockbox
secure briefcase
secure crate
secure closet
library computer
claim console
cyborg
apc
PACMAN gen
emitter
rd computer
rd server
shuttle computer
RCS