Printrbot bowden remix

I have changed the X axis pieces to adapt the printbot to E3D V6 bowden. Also I've changed the carriage of the X axis to avoid vibrations and I've added a layer fan. Last but not least, I have added a end of races on all axes and a guide for the filament to use it with this spool holder https://www.thingiverse.com/thing:1027730