Move VirtualFluids header to src.
Add CI file and add files, only existing in the open source version.

Therefore the muparser cmakeLists.txt was used, but a modified:
 - name is corresponding to the original file: muparser (in lowercases)
 - removed the install
 - adds public include directory : CMAKE_CURRENT_SOURCE_DIR/include.  --> also adapt the include from the dependent fles.
 - adds link to OpemMP

CXX 11 is now required. (CMake throws an error if cpp11 is not available).

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.

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

Remove unused stuff and the global include from VirtualFluidsDefinition.h. Adds missing export includes.

Adds authors and contributing file. Clean up the readme file.
Set the minimum cmake version to 3.13 according to the readme entry.
Set the options BUILD_VF_CPU, BUILD_VF_GPU and BUILD_VF_UNIT_TEST to OFF by default.

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

Changed the setting the compiler options to the new cmake function: target_compile_options