Changed EclipseGridParser::saveEGRID() to take globalCells input

The EclipseGridParser::saveEGRID() takes an input argument (const int * globalCell) which is used ta map out ACTNUM. This is to ensure that the saved ACTNUM field is correct with respect to cells which have been deactivated by opm-core.

Observe that the methods saveINIT() and saveEGRID_INIT() are not really functional after this PR; but they have no callers.

This PR is a start of a fix to: https://github.com/OPM/opm-upscaling/issues/69, a similar PR will come for opm-porsol.