now, all the beauty of that part of the code can be admired in
initStateEquil.hpp.
During this exercise, I stumbled over some serious code-quality issues
like a different order of the template arguments for the declaration
and the definition, mismatching argument names and no forward
definition of some functions. besides this, some functions were
already defined in the non-_impl.hpp file and EquilibrationHelpers.hpp
used that approach from the outset.
this just moves the hydrostatic equilibrium code from its historc
location at opm/core to ebos/equil and adds minimal changes to make it
compile. this allows to clean up that code without disturbing the
legacy simulators.