Filament rod holder

For easier exchange of the filament spool on the original Anet A8 filament holder, we designed a small part which fits onto the filament holder rod bed.

With this part it is possible to get rid of the both fixation M8 nuts, because the rod is fixed in the new holder.

This part fits in the original acrylic holder of the Anet A8 and should also work with
[Anet A8, Omni m505, Filament roll stand](https://www.thingiverse.com/thing:1512184) (but not tested yet).