Minimalist Duplo - Brio, IKEA, Wooden Train adapter remix for better printability

This model improves on the printability of the original model by András Bognár : Added a cross on the bottom that significantly improves the strenght of the peg. I could break the original with my finger, there's no chance that happens with this remix. Turned the model upside down and added 45 degree angles, that way the model is printable without supports. Added a 0.5mm drop in the hole at the top to force the slicer to make straight bridges, this improves printability