Create python bindings for the backend

[multun]

We need a way to run interact with simulations from a python interface, either using FFI, or a networking api.

This interface will need to:

• be able to manually run the simulation event loop, so we can stop at critical times
• be able to change the ordering of trains at junctions
• inject delays (we have to decide whether to pick a single way to do it or implement multiple failure modes)
• observe train delays at a given time

[flomonster]

We need to make train disappear once they achieved their path. It could be an option given in the simulation payload.