added second forall loop again, since updating location needs to be done in a separate step. To calc the force of one Particle, the locations of all other Particles (in the last simulationstep) are needed. Immediately updating the location leads to corrupt results

Repo: Manual reset to origin/master to clean up repo for merge request to upstream. Summary of changes: added input validation, fixed race conditions, major refactoring, improved readability and correctness, re-formatting of code.

DSDE sample (n-body): fixed issue with vanishing particles (mpitype_part_free_send was resetting n_receivers to 0, causing MPI_Testall to signal completion of local sends immediately).

Added initial halo_exchange sample (unstructured grids) and dynamic_sparse_data_exchange (n-body methods)