Refactor/tidy __main__ to feed properly into generate_graphs()

[geekscrapy]

There is some code overlap in the main section that should be included in generate_graphs() - most functionality should be in generate_graphs() anyway.

This will be a fairly mixed commit, so please can contributors hold off pull requests for the main and generate_graphs() until I have refactored the code.

Thanks!

[geekscrapy]

Completed in 494079a