Moved Simulation::init() to Constructor, Simulation:free() to destructor.

This is a refactoring of Simulation to make the class a bit safer.

This means: I moved the logic of Simulation::init() to the constructor, Simulation:free() to destructor and exchanged some members with unique_ptr instances. With that its now possible to just start a simulation with

Simulation sim(/*passing all necessary objects ... */);
sim.run();

Afterwards the necessary clean up routines are done automatically with the destruction of Simulation.

@m.schoenherr @a.wellmann This MR implies the adaption of your other applications according to DrivenCavity.

This diff also contains the removal of a lot of dangling whitespaces. This unfortunately blurs the diff somewhat. You might want to look at simulation directly and not the diff.