Rudder pedal mods

Many thanks to Taumelscheibe and others for all the work. Here are some extensions I have implemented.

bearing_holder_2020.stl
- Added break-away tabs that turn overhangs into bridges so no support material is needed when printing.
- Added fillet to round the edges.

2020_endcap.stl
- An endcap that works with V slot 2020 extrusions.

magnet_holder.stl
- Added a thin layer which converts overhangs to bridges so no support material is needed when printing. Leave this in or drill through it.

MagnetGrubScrew.stl
- The holes for the magnets in the magnet holder are fairly loose. This plastic grub screw fits a bit more tightly and holds the magnets in place.

bearing_holder_2020.Bracket.stl
- Inspired by FastIndy's replacement for the 2040 bearing holder.
- Replaces the 2040 extrusion with a 2020 extrusion. The 2040 is unneeded and more expensive. Fewer screws too.
- Moved the bracket arms into line with the bearings as this is where the stress is.
- Only 30mm high (whi