Enclosure for Duet + optional DueX4 electronics

This is a remix of bobtidey's design to accommodate the Duet and optionally the DueX4 expansion board. The DueX4 is mounted face down (after connecting all wires except the power wires) and then the Duet is mounted behind it. Also provided is a Duet enclosure suitable for use on the Mini Kossel as in my blog entry http://miscsolutions.wordpress.com/2015/01/04/upgrading-the-mini-kossel-to-duet-electronics-part-1-hardware/.