Power supply cover - improved version 2

This is an improved version of my earlier [power supply cover using Molex connectors](http://www.thingiverse.com/thing:182462). As most has remained the same, I only dwell on the improvements relative to the initial version:


- An *air flow grid* on the lower front side allows for better ventilation.
- The Molex connector can now be secured with *clips* so that they don't have to be glued in.
- A new cut-out is provided for the *voltage adjustment trimpot*.



Gi