Bed levelling driver

Using my screwdriver to level the bed is not really comfortable, so this item uses a little neodimium magnet (`6mm` diameter x `2.75mm` thickness) to act as a short driver which can be used with the standard `6mm` hexagonal inserts.

The magnet is also very useful to attach this tool to the frame anywhere where you have a magnetic metal (screws, motor body, etc...).

I printed it at `0.3mm` pausing the print at 13th layer to push the magnet in place, then resume the print to have the magnet