Moved Simulation::init() to Constructor, Simulation:free() to destructor and exchanged some members of Simulation with unique_ptr instances.

added WallModelProbe, replaced PostProcessingVariable with Statistic in Probe (and all derived classes) and added some documentation

Added SG model to StressBC, added Timer-class which wraps existing timer in Simulation, added round-off correction in TurbulentViscosityCumulantK17CompChim_Device (testing ongoing)