Added first attempt at Duet+Duet4X enclosure
Corrections to Duet_X4 enclosure

Moved X4 lower standoffs an extra 2mm apart to match X4 board
Increased Duet standoff radius by 0.1mm because slic3r was generating 2
circles to print it instead of 3
Added extra 1mm clearance for ribbon cable at top of box when X4 option
is enabled