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.

Remove VirtualFluidsDefinitions.h header file.
Remove redundant compiler definitions from gpu.cmake.

Add public target include directories to the cmake targets. Therefore the IncludeList.cmake files are not necessary anymore.
ADapt the export macros in the gks libraries.
Add 3rd/vtk helper cmake macro.
Gorup muparser into 3rd subfolder in visual studio project.

Make the cmake project more flexible while removing the CMAKE_SOURCE_DIR usage.