Remove check for ZeroMQ.
ZeroMQ isn't needed any longer.

Fix installation of externals when using Spack.
Pass extra flags flags to NicaFemto configuration if needed.
Patch ipc source code. Add missing include file.
Cleanup .gitignore in externals.

Fix linking of CbmGlobalTraking library.
Add missing link directory. In normal installation Vc probably was found in the
ROOT installation. With Spack ROOT is build without builtin Vc.

Use correct syntax for function call.
With the latest FairMQ version the old backward compatibility layer was
removed. Use now the new syntax to change the state.

The externally loaded spadic package is now longer required for the current spadic versions
Hence, it can be removed from the cbmroot master and future release versions

Add support for C++17
Check for c++ version c++11 or above (11, 14 or 17). With this change it
becomes possible to compile CbmRoot with C++17.

Add missing library.
The FairMQ state machine is now in an extra library which has to be added
for linking when using FairSoft nov20. Test if the library exist and create
the list of dependencies accordingly.

Add missing include directory.
VMC is not any longer included in ROOT but a standealone package, so the
include directory has to be added such that the header files are found.

Add gtest as an optional external package.
With the latest version of FairSoft googletest was removed due to a
recommendation of the gtest developers. Since gtest is no longer part of
FairSoft we have to provide an own version which is compiled as external
project.

Add proper dependency to external gtest project
This dependency is needed to compile the test only if the gtest library is
already available.

Fix compilation error with FairRoot v18.4.2 on macosx
In FairRoot v18.4.2 some linker settings were removed from the CMake setup.
This breaks the compilation of CbmRoot. Put back the needed seetings for the
linker on macosx in our build system.

Fix NicaFemto installation