D-BOT single Z motor upgrade

This remix of the D-BOT core XY, allow the use of only a single motor to have the lead screws perfectly synchronized.

Used:
N°1 Nema 17 1.8deg 44Ncm (62.3oz.in) 42x42x48mm
N°3 GT2 timing pulley 36 tooth, 6mm width, 5mm bored
N°1 GT2 closed loop belt, 6mm width, 1114mm lenght (there is space for different lenghts)
N°4 F623ZZ flange bushing ball bearings F623ZZ 3*10*4 mm (advanced from the printer build)
N°4 M3 washers (to put between the flanged bearings)
N°4 625ZZ ball bear