Investigate tool for padding of grid model

[magnesj]

opm-flow team has a command line tool for padding of a grid model. Investigate this tool and consider how this can be used from ResInsight. Consider use as external tool with GUI in ResInsight or refactor the code internally in ResInsight.

https://github.com/hnil/opm-flowgeomechanics/blob/geomech_hypre_cgal/examples/padmodel.cpp

[kriben]

The padmodel.cpp code looks suitable for our purpose: after extracting the sector model and modifying the deck we can just call a slightly modified manipulate_decks method. We will need to pass in the already loaded deck and the padding parameters instead of file paths, but that is just small details.

@bska ResInsight depends on opm-common already. Could it make sense to move it there? I volunteer to do the work, and add test cases++.