Prototype support clone cells in computational grid generation-node numbering (fortran)

[GolnesaK]

For the prototype / dev version, we treat all obstacles as cutlines. In a later stage, we may either introduce a new layer in the schematisation (clone_cell_cutline) or add a boolean attribute to the obstacle layer (is_clone_cell_cutline).

Implement the following in threedigrid-builder, fortran part:

• number the cells based on the area mask
  • every clone cell domain needs to contain at least 1 data pixel
• reorder the 2D nodes (old host cells might be left out)