this is not needed anymore because the grid manager is no longer a
singleton and the grid is thus is always destructed before
MPI_Finalize() is called.
i.e., removing redundant namespace open- and closings due to the fact
that the property system now resides in the 'Ewoms' namspace instead
of in 'Opm', and making the headercheck work for all headers.
because "manager" sounds less religious than "creator" and the
GridCreators did all kinds of other stuff besides creating the grid.
this patch also gets rid of the static function inside these classes,
which should make them easier to understand...
