Wearable Orange Pi Zero Case

Based on a great design by https://www.thingiverse.com/xoan and https://www.thingiverse.com/farrukh. Changes include:

* Snap in (no more screws required!)
* Vertical and horizontal antenna option (near the ethernet socket)
* The bottom part has some hooks for strapping the case onto a USB-battery-pack..
* Made the slot for the USB-connector 0.5mm wider
* Added a hole above the LEDs, so that we can peek inside.
* Re-modelled the case from scratch, excessively using the sketcher workbench. Beware: done with freecad-daily 0.17 rev 12495!

To mount the orange pi on a battery pack, you can use clip-72-16.stl -- Either scale the STL file by a few percent up and down in your scaler (X, Y, only, do not scale z.) to make it fit your battery pack, or change the dimensions in the fcstd file and re-generate the battery clip. Additionally, there is a belt-clip.std which goes on the other side of the battery pack, where the c-clip is thinnest. Using the belt clip, the entire assembly ca