Added methods to export the ZCORN, COORD and ACTNUM keywords from the EclipseGrid.
Added functionality to export MAPAXES data.
Merge branch 'eclipsegrid-export' of https://github.com/joakim-hove/opm-parser into check_filesystem_case_sensitiveness

* 'eclipsegrid-export' of https://github.com/joakim-hove/opm-parser:
  Added functionality to export MAPAXES data.
  Added methods to export the ZCORN, COORD and ACTNUM keywords from the EclipseGrid.