Adding CAD files for laser cutting the perspex cube.

Files added:
   cube1.dxf
   cube2.dxf
   cube3.dxf
Added labels and back holes.

Files modified:
   cube1.dxf
   cube2.dxf
   cube3.dxf
Resized each face of the cube to be 130mm square. Added holes
for beaglebone sockets.

Files modified:
   cube1.dxf
   cube2.dxf
   cube3.dxf