Add functionality for nested hybrid grids

[jcrivenaes]

This task is based on the following workflow

• Make a region in the 3D grid that shall be refined
• Do refinement if the grid wihin this region. This involves a 'trick' which is to extend the grid in IJK coordinates, but let those coordinates overlap in real coorinates with the current grid
• Do a proper manipulation of ACTNUM for the hybrid case
• Set up NNCS to connect the hybrid grid with the original grid