Synchronous test for grid agent in center position

[ckittl]

As of #111, the GridAgent resp. DBFSAlgorithm uses the dispatcher from actor context. For execution of power flow calculation.

However, using the TestFSMRef for synchronous testing, the configured dispatcher is explicitly overridden to `CallingThreadDispatcher' utilizing only the calling thread. However, this poses the risk of dead locks, which we obviously fell in.

Synchronous test currently is disabled, as we intend to refactor to akka typed and therefore the test also needs refactoring. However, if that is done, re-implement a synchronous test!