PSU mount for Microcube

This mount allow to fix the PSU of your microcube inside the printer structure.

STL files are for a PSU of 170x85x40mm (I'm using [this one](https://www.banggood.com/12V-10A-120W-Switching-Power-Supply-Convert-Adaptor-For-CCTV-Camera-p-943162.html?rmmds=myorder)).
But source file (power_supply_holder.scad) is provided if you want to ajust it to different PSU sizes.

There is two STL provided for front holder: one for basic microcube, and another one ("narrow") compatible with a second z