Collapsible cup

Tested to be water tight, also after folding some 10-20 times. Quite small in the STL file (30mm tall, 30 mm diameter in top). Change height/diameter in included FreeCAD file to scale up nicely (if scalling whole model, might become too stiff to fold nicely)

**WIP:**

* Currently does not stay collapsed by itself
* The top-most ring does not fold nicely

Print in NinjaFlex, or similar flexible material.