Complete train signal bus with example builds.

Allows chaining of any number of locomotives and cars in any order.
Take control from any seat of any locomotive and drive the other locs remotely in unison.

Includes simulated air brake system with emergency braking. Reimplemented and refined as Lua script after original Railway Air Brake Controler: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2088331117

Air braking system is simulated after real life as follows:
The controling locomotive supplies air on the main bus.
Every car has a local reservoir which is used for braking and toped up from the main bus when possible/connected.
The brake cylinders are filled from the reservoir upon braking.
Disconnected cars will brake automatically using the reservoir.
Braking and releasing brakes takes a small amount of time while pressure builds up / is vented.

Detailed bus signal information here: https://docs.google.com/spreadsheets/d/19kbptYs2C0DWif8XPlurEwSsASCXRiweb_CFvQE7qlo/edit?usp=sharing

Use, change, include in any way you like.