Update the scripts to copy from geomodel grid to ertbox grid to handle individual ertbox per geomodel zone

[oddvarlia]

Background:
Coming version of ERT will be able to specify individual ertbox definition per 3D field parameter. The current version with one common ertbox grid to be used for all field parameters will continue to work if no individual ertbox per field parameter is specified. But the purpose of having individual ertbox definition per field (in practice per geomodel zone) is to reduce unnecessary use of memory, diskspace and CPU time. The advantage of individually sized ertbox (typically number of layers) is largest when the geomodel zones with field parameters have very different number of layers.

Proposed extension of copy_rms_param_to_ertbox_grid.py is:

• Enable the possibility to specify different ertbox grid per geological zone but also keep the option to have one common ertbox grid.