Electric locomotive for Ikea Lillabo/Brio train (USB rechargeable)

**There is now a [newer and better version](https://www.thingiverse.com/thing:3949927) of this thing.**

This is inspired by MilanGajic's electric locomotive. I wanted it to be as compact as possible (to fit in the Lillabo tunnel) while looking like a (kid's idea of a) locomotive (and in particular having a nice cow plow at the front end!). I still consider this as work-in-progress, see below.

Good points of this model:
- it works!
- it (just) fits under the Lillabo tunnel!
- parts ju