Print properties of graph neatly

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

cost_function.py

@@ -103,7 +103,12 @@ print('Loading gt file...')
 g = graph_tool.Graph()
 g.load('segmented.gt')
 t1 = time.perf_counter()
-print(f'Loading done: {g}')
+print("Input graph:")
+print("Number of vertices:", g.num_vertices())
+print("Number of edges:", g.num_edges())
+print("Internal properties:")
+g.list_properties()
+print('Loading done...')
 timings.write(f"loading: {t1 - t0} s\n")
 timings.close()