A bigger fuel pod

after upgrading to latest git i noticed it now takes 2 fuel tanks for 1 extra jump with my kestrel. so i decided to create a bigger type of fuel pod. I doubled the fuel and tripled the price. i also made it a medium sized item so it cannot be used in small ships. 

![largefuelpod2](https://f.cloud.github.com/assets/153243/669823/10925b88-d835-11e2-817d-d686fe19f6bb.png)

the icon is a quick and dirty copy/paste but i think it looks okay. ifnot i'm sure some artist can make a very nice one in no time.