Swash Wrapper postprocess flags

[fernanqv]

If you use the force flag when running postprocess_cases in swash wrapper the force flag is not passed to postprocess_case. It would be advisable to add a force flag to postprocess case and in case is set, delete the previous postprocessed files (output.nc and output_postprocessed.nc).

Besides, if output_postprocessed.nc is created and force is not set it should not recreate the file. Now it recreates it although the file exists. This should be fixed.

[tausiaj]

We are working on it, also trying to introduce parallel processing in postprocessing (check notebooks vs python executions)

[tausiaj]

Check what happens when passing force, but interpreted not as kwargs.