Massive pep8/pyflakes cleanup

The pyflakes and pep8 checks should now run automatically when Travis CI builds run. I've documented which flags are ignored in .travis.yml (e.g. line length checks).
I'm with you. Where we need to fix it is in https://github.com/18F/foia-hub/blob/master/foia_hub/settings/test.py, at the top. It's not clear to me how to elegantly do that.