Gearbox remix version 1

This is a very minor remix of mjiael08's awesome gearbox design:

https://www.thingiverse.com/thing:3726483

I remixed a couple of parts to improve gear meshing and fit as well as accomodate a LEGO motor.

C055 - modified drive gear so that a LEGO motor can drive it
C050 - reduced diameter slightly to fit better
C024, C030, C036 - modified gear teeth to improve fit
C07, C019 - shortened shaft so it does not extend past frame and added an adapter to fit a LEGO shaft
C001 - added small groove to fix contact with gear C004