Add capabilities to Comm structure

[bartgol]

Is your feature request related to a problem? Please describe.
Right now the Comm struct is simply storing rank and size of the comm group. But it might be helpful to add some utility functions, like reduceAll, or split. This would make downstream code simpler to read (hide heavy MPI calls).

Describe the solution you'd like
Add "simple" and "common" mpi pattern utilities (reduce, broadcast, split).