Prusa i3 box for Megatronics v3

This is a box to host Megatronics v3 board (mine is rev. E). The box is designed to be mounted on the back of a 6mm aluminium frame using existing holes.

##Features

- clips to keep stepper and other cabling in place
- clips on cover to keep fan cable in place
- three large entry windows on bottom for air and cable enter
- almost open back for cooling
- 50x50 fan mount (to cool XYZ stepper driver and power mosfet) with spacers to avoid contact with cover
- open top to let air circ