After recent discussion on IRC, I'd like to propose the following plan
for integrating the simulation core (minimal_simulator branch in my
repository) and the rest of the code.
In the minimal_simulator branch test-cases should be defined, just as
the GUI would use the simulator core. This way for the GUI part the
usage of the simulator can be defined, and also for the simulator
part, the tests should demonstrate that the simulator is working.
Feel free to propose tests for using the simulator. The API can be
observed in the existing tests.