rather, only set it where we want to use it. this avoids including
eclwellmanager.hh and eclpeacemanwell.hh unnecessarily in
simulator objects (where BlackoilWellModel is used).
these variants should cover most of the common use cases. That said,
there are no plans to provide simulators for combinations of blackoil
extensions or a "multiplexing" simulator like `flow`: If someone is
interested in e.g., an oil-water simulator with polymer and energy
enabled, a separate self-compiled executable should be added locally.
