New pulley for X-Y axis Geeetech Prusa i3 X

This pulley is a remix of http://www.thingiverse.com/thing:1264451 from Rom1330.
My version uses two 608ZZ bearing instead of one, to give a larger area for the belt.
The pulley can be used for X and Y axis with no need of modifications.
Made this because the original bearings were too weak.