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

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

and refactore this function for better readability

and refactoring this function for better readability

Remove them from LevelGridBuilder

For communication after interpolation fine to coarse

Find all send and recv indices which also are interface cells fine to coarse, coarse (iCellFCC).
Move them to the front of the vector of send and recv indices. Return their number as well.

Warning: [-Wbackslash-newline-escape]
https://stackoverflow.com/questions/31673945/clang-backslash-and-newline-separated-by-space-in-single-line-comment

Made VF_GPU work with the "new" cmake