Refactor Actuator Farm

I split the actuator farm into two classes, one that only contains the core functionality necessary to couple it to an outside library such as WiFI and one that works on its own. The reference system has changed from the local to the global reference frame. That reduces the complexity and necessary data significantly. It also simplifies future implementations of towers or actuator disks significantly.

Because the computation changes, the Actuator Line regression test has to be updated. The quite large deviations in some points result from a bug in the old version that cut off the spreading of the forces too early.