Adding retracted legs sprites for the Suspension Field Generator (xenoarch)

If I bang my head hard enough on Github, maybe I'll get my changes into the game eventually.
Okay so I think I've finally gotten the hang of it. I used Tortoise a few years ago so I'm not completely stranger to all that but...oh anyway...here's a copypasta of that failcommit I posted about an hour in the  Baystation12:master section :

So we get a visual feedback that the Generator is fixed or not. Not to mention, we get a message telling that "the stabilising legs are wrenched into place" or "up against the body" but the sprite itself doesn't change at all.
![legs](https://cloud.githubusercontent.com/assets/7573912/2964553/c28138e0-dae7-11e3-9162-00a346cb3673.png)
(there are also ones for when the cover is opened or the cell is missing)