Remove debugging ls. Activate double accuracy for the numerical tests. Deactivate 256 & 512 grid sizes.

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.

no changes in configFiles for numerical tests necessary

numerical Tests of K15 and viscosity 10^-2 passes 42 of 60 tests, for the lower viscosities it has to pass 60 of 60 tests
computation time for every viscosity is ~35h on one Geforce 1080ti

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

Exchange DEPENDS (which links everything private) variable with PUBLIC_LINK and PRIVATE_LINK. Therefore VirtualFluidsCPU is linking everything public know. Everything else is still linking private.