It is not used and it complicates processing the edgelist.

Create properties in `cost_function.py` rather than in
`segments.py`. We do not use these properties in `segments.py`.

The property in the input edgelist is not the non-local cost function.

Simply printing g displays the address of the graph, which may change
between runs. This was not convenient for the comparison of runs.

Motivation: being able to choose a different output format at
run-time. We use the graphml format for the automated test, because
graphml is a text format, so we can compare the results of two runs.

To be able to read edgelists output by the Fortran program.

They had the default values.

Remove unused `e_overestim`, `d_init`, `orientation`.