Use list() with component generators

Update to strongly connected component algorithm to return generator requries explicit use of list() in simple_cycles()
Whitespace and formatting cleanup
Avoid use of list() in condensation
Merge pull request #1 from hagberg/francis-liberty-issue_973_generators_copy

hagberg added some fixes:
Fix cycles algorithm by adding list()
Clean whitespace and formatting
Rework condensation to avoid use of list()