the pointer is allocated in the ctor, so the fact that it is a unique_ptr
can be kept as an implementation detail. furthermore, the previous
accessor did not properly enforce constness, as a const unique_ptr<EclWriter>
only applies const to the pointer class, not the data the pointer points to.
we do the compostional related in GenericOutputBlackoilModule to minimize the code change.
there needs to be refatoring for GenericOutputBlackoilModule to split
the black oil and compostional related.
currently, it looks the value for ZMF is based on XMF and YMF.
ideally, the ZMF is part of the primary varialbes, it does not need to
be calculated based on XMF and YMF.
there is some refactoring that we can do here.
so the FlowProblemComp can output ecl style output.
it duplicates the OutputBlackoilModule and GenericOutputBlackoilModule
for compositional related output for now.
Arne Morten Kvarving
Kai Bao