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

Add gpu options to root cmake. Add the cmake option for passing the path to the numerial tests. Add git clone test to the CI.

Change in cmake: When BUILDTYPE is not defined in vf_add_library(), a library is build regarding the CMAKE_BUILDY_TYPE.

Add a fix for the numerical tests, where all compile definitions were overwritten by set_target_properties().

Remove unused Project command in cpu.cmake and gpu.cmake