Add .pep8 file from edx-platform

Adds in the .pep8 file from edx-platform.

I would also like to enforce 120 characters limit on XBlock (by enabling Pylint warning C0301). 

@wedaly @jzoldak 

Tangentially, I would like to discuss when we should enable this warning on edx-platform - consensus in the LMS room is that we really ought to do this (120 characters is a lot!) but would need test eng to sign off on this, as undoubtably this would increase our pylint count. If not today, then perhaps would be good to think of when to make this change.

For what it's worth, enabling C0301 in to edx-platform adds just shy of 500 additional pylint violations.