How to run BornAgain on a cluster

To run BornAgain on multiple nodes, i.e. processors on different motherboards, rudimentary support for OpenMPI is implemented. It concentrates on Monte-Carlo simulations, and is demonstrated by the example Tests/Functional/Core/MPI/mpitest.cpp.

Some more info can be found in this discussion: https://github.com/scgmlz/BornAgain/issues/914.