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)

In copyEdgeNodes the nodes were copied to the wrong places of the send vector. The problem was that the full vector sendProcessNeighborHostAllNodes was used for copying instead of the shorter vector sendProcessNeighborHostAfterFtoC

Fixed periodicity issue by addind STOPPER_OUT_OF_GRID_PERIODIC flag. Further preparaions for stress BC