calculated and stored as private data members in EclipseGrid.
The API for the class is unchanged except for some minor changes for exportACTNUM, exportZCORN and exportCOORD.
These changes have triggered some very few modifications in the opm-grid and opm-simulators repo.
This makes the facility usable for the restart read/write code.
Specifically, import the I/O classes into namespace Opm::ecl, and
place the files in physical location opm/io/eclipse, and move the
test utilities to new top-level directory 'test_util/'. While here,
discontinue the 'testutil' static library since most of its features
are now available in the main 'opmcommon' library. This does entail
compiling a few of the test_util/ CPP files multiple times, and
adding the objects to each executable independently.
