[Done] Electrical substations

Took advice from commenters from #8677 and made some power substations. This took a good while to throw together, lol. They are filled with zombie technicians and shockers. The equipment in the substations are also explosive as hell, which is rather fun with the shockers firing electrical arcs everywhere.  

![Booyah](https://cloud.githubusercontent.com/assets/4348451/4031978/02f1499e-2c6c-11e4-8591-9cd4b7545d34.png)

I couldn't really figure out how the overmap specials worked, but I messed around with the settings for the stations for about an hour until I got the spawning relatively close to cities, and spawning not too often, though you may find 2 or 3 to some larger cities.

Now that I understand the overmap spawns a bit better, I'll work on transferring the SAI's from #8677 to an overmap special instead of into the reigonal settings.