Tunnels for trains

Very instable at the moment. Any help to stabilize it is appreciated.

How to build a simple tunnel:
https://www.youtube.com/watch?v=p8ZDI6xNr5M

TODO

• fix all the cases of decoupling and hopefully remove the need to slow down trains
• fix transition between manual_mode and auto. move driver to previous controlLoco on auto->manual
• fix/replace the quadtree implementation ...
• mod configuration. resources on underground, diggy, max underground level
• editing trains that are partially in tunnels causes problems