[Ready] Large power substations

After a couple of days I finally got around to adding the 2x2 substation, with a new "mini-boss".

Nice, big open area between the equipment (unlike the small station), but with more room for stuff to go crazy, like with the new enemy.

(Didn't want to spoil it for anyone, so it's not in the picture)
This is pretty much the layout.
![large station](https://cloud.githubusercontent.com/assets/4348451/4104123/8a2c9f52-3181-11e4-8d5b-661dfcaa549e.png)

There a particular reason for so many substations?  My initial impression on looking at the overmap was "WOW that's a lot of substations,", and I'm thinking that tuning these down a bit might be a better way to go.