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 buried inside the handle.

My insert fits perfectly, but it's easy to adapt to other inserts.