Implement feedback loop

@aborissov I have implemented the feedback functions in this merge request. If you have any question about it, I am always available on slack. I have also pushed my SedovBlast_3D example with a star at the center in order to generate the blast. You will still need to implement the task dependency and default feedback scheme.

@matthieu nothing fancy here. I am just applying the runner_doiact.h trick to runner_doiact_stars.h, removing the timers and pushed my example that consists mainly in a copy/paste of SedovBlast_3D.