Robo3D Enclosure

This is a derivative of Mike Kelly's enclosure over at http://forums.robo3dprinter.com/index.php?threads/mike-kellys-robo3d-enclosure.2712/
I cleaned it up and changed the design so that you can use either .236" or .25" thick material and it can be assembled with just M3 nuts and bolts (20mm or 18mm). This makes it very strong. It also allows you to change out just one part if you happen to damage it one way or another.
I also unified the design so you don't have subtle differences between