Parameterized Skadis Universal ring holder

I started off with [https://www.thingiverse.com/thing:5388605](ripetomatofetish's great round holder for the universal Ikea Skadis hooks). However I was missing a little bit of offset between the ring and the baseplate. In the end I did a major overhaul and added a number of parameters to easily adapt it to different needs.

Requires one [https://www.thingiverse.com/thing:2853257](Skadis_Universal_Hook from CSD Salzburg's IKEA SKADIS Universal Hook Set).
No support needed.

New features include:
- Parametric distance between ring and base
- Parametric height to decouple ring thickness from ring height
- Parametric cutout at the front of the ring (Handy for things that won't fit through the ring from the top, like my chisels)
- curved part of the connector scales together with the ring height to give a better visual impression
- in case the ring height gets too big, the curvature of the connector is minimized to prevent obstruction of the mounting hole
- added assertions to c