Fixes siemens_coefficent not affecting shock damage

Currently, siemens_coefficent has no effect unless it is 0. This meant that the siemens_coefficent of clothing was not being used, and in particular, budget insulated gloves were useless.

This also cleans up electrocute_act(), and allows the option of electrocuting specific defence zones.
Stuns are not meant to be universal, stun immunity is fine imo. Lethals exist. Downstream will want to be more careful with this than main Bay.