Improve code styling

[ChillarAnand]

It is hard to read code in editors as it is not formatted correctly. We can use tools like autopep8, yapf to automatically fix those issues.

Also, add flake8 to Travis.

[zuphilip]

PEP8 coding style sounds generally good for me. But I think this would involve in a huge amount of changes through all files. Some time ago I started to add more unit tests to increase also coverage and I would feel more save when we have them in place, before improving coding style. Moreover, we also have some issues with imports, I certainly would like to fix first, see #206.

@tmbdev, @kba, @QuLogic, @amitdo, what do you think about PEP8 coding style?

[zuphilip]

(moved unrelated comments by @Christophered to temporarily place https://gist.github.com/zuphilip/6dabb222b6fcd4c2663ba0d9e796a915 )

[zuphilip]

Some of the issues about the coding style should be improved. If you encounter anything specific which should be urgently improved then just let us know, or create a PR. Closing this issue now.