Prusa i3 MK2, MK2S, MK2.5: Y axis front corner replacement - reinforced.

This is a remix of the front part of changfrancis's Y Axis corner block repacement.
I loved the idea, and these parts makes mk2(s) so much easier to assemble. However i noticed too much springiness when tightening the front part and this caused inaccuracies. So this is a reinforced front replacement part.

Changes:
Reinforced part to make it stiffer. Changed holediameter for rods from 8.8mm to 8.1, to make tolerances tighter and preventing flex inside the channels.
Closed rod channel more p