Improve interpretability of exported IIS

[felixblanke]

ad802a0 added the feature that for the gurobi optimizer in case of infeasability an irreducible inconsistend subsystem is exported. This helps in the search for inconsistencies in the input data. However, the resulting ILP file is somewhat cryptic.

It would be helpful to add a postprocessing which improves the interpretability of the IIS files.