Fix up code to pass pep8 and add flake8 as a build check

[nigelmegitt]

There's a variety of coding styles used in the LIT at the moment, not too many, but also there's some lack of consistency, and lack of guidance to contributors for how to format the code they add.

Suggest doing a pass-through of the whole library to pass pep8, using the flake8 qa checker, and then add flake8 to the travisCI build script to check that new pull requests don't break it. Also add to the contributing readme to explain that we use pep8.