update generate_traversal_graph to decide traversal for epsilon and critical events

[abegehr]

first remove (generate_traversal_graph):
# does: if only one traversal, just use it if len(traversals) <= 3: graph[0].add((1, (0, 0))) graph[1].add((2, (0, 0))) return graph, traversals
and (traverse_recursive):
elif len(critical_traversals) == 1: # if only one critical event is found …
then fix errors