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.
```there are several items which have a coeff of 0, the way this is written would make you immune to stuns if you wear one of those.```

That's the idea. If you don't want an item to block stuns, then change it's siemens_coefficient. It's not like it's used for anything else at the moment (with the exception of gloves).