auto-rewind adapter with fingers

This is my remix of a spool holder adapter with tension fingers. That should increase the range where the adapter works compared to the plain version.

There are a bunch of magic values so it'll probably only work with the 44mm spool holder "standard" I'm using for all of my spring cores.

uploaded v4 on 2019-01-02; the finger thickness is much better so it is springy, removed a bunch of code, made the fingers basically full-length. It also embosses the ID/OD on the flange.