Create Gates_Threading.py

Python code for Raspberry Pi level crossing project.
For my first attempt at this project I have used used 2 stepper motor a bunch of coloured LEDs, a push to make switch and a piezoelectric buzzer for the siren, along with some wood work from Rich Cooper see https://www.youtube.com/watch?v=BMJyFkuUDO4
A new version has been requested (by my son) with 4 gates and automated detection of the train passing a specific point as well as the manual button control.