Consider using a PEP 8 checker to clean up the codebase

[jlebon]

As discussed here, it would be nice if we cleaned up the codebase using a PEP8 checker. It remains to be seen which tool we should use (there seem to be many similar checkers available).

Note however, as pointed out in this SO answer, pep8-ifying a whole codebase has some drawbacks. Maybe we should instead enforce a rule that from now on, new commits must be PEP8 compliant.

[miabbott]

I'm in favor of enforcing PEP8 compliance for new commits.

I don't think our codebase would suffer too greatly in terms of merge conflicts or breakage of git blame, so I'm also not opposed to PEP8'ing the whole thing.

However, the pep8radius tool looks like it might be a more conservative option.

[aweiteka]

It would be quite trivial to add a travis CI job to check PEP8 on each PR. We could also have a job to do a dry-run on all steps. Low-hanging fruit. :)