Ultimate Stiffness Y Axis Tensioner and pulley for Wanhao Duplicator i3

The Y-axis on the i3 machines have far too much compliance giving rise to ringing artefacts - Very apparent when the printhead has to negotiate sharp turns/corners.

There are 2 key sources for this compliance:

1. Spring style belt tensioners - these work intrinsically by introducing compliance (bad idea)!
2. The flimsy idler pulley mount. The narrow base, tall geometry and sheet metal mounting all rob rigidity.

Existing tensioners on Thingiverse do away with the stock spring tensio