use mpi4py with dill to allow serialization of onebody states

Merged Kloss requested to merge mpi_pickle into master

the onebody solver uses closures and also a cython type that prevents mpi4py to use pickle. changing the mpi4py protocoll to dill solves the problem with the closures and with the removed the cython type, no negative impact on speed has been observed.

Edited by Kloss

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