12V PSU safety cover + 120mm fan modification

Remix of [12V PSU case cover with 120mm fan](https://www.thingiverse.com/thing:2203093) by jolbars.
Added:
* terminals to PSU for wire safety
* 120mm fan dust cover
* mount for PSU onto 2020 extrusion.

Your bed has to be at least 245 x 120mm to print (Supports Tevo Turantula Large bed)

**PSU Setup**
* 1 x PSU Cover
* 2 x M3*12mm Screw (To screw to PSU)
* 1 x [Rocker Switch (KCD3)](https://is.alicdn.com/img/pb/270/936/666/666936270_416.jpg) (rated for mains)
* 1 x [C14 Male Connec