these objects are only used by flow_legacy, so not having to deal with
them anymore lets non-legacy flow avoid to jump through a lot of hoops
for the sake of having a common API.
this required a fork of the NonlinearSolver and AdaptiveTimeStepping
classes. this is not a problem because the original classes would get
pruned to look like the new ones once flow_legacy gets moved out of
the opm-simulators module.
Previously the substep summary reports were cumulative, misleading the user.
Also, made output a little more compact and readable, ensuring numbers line up
unless unusually many digits are needed for times and iteration counts.
That version does not provide a default constructor for
CollectiveCommunication, Therefore we now use
MPIHelper::getCollectiveCommunication() for the default
constructor argument.
