Add flake8 to test suite

[RobRuana]

As a developer, I want a machine to double check my work to ensure that I am committing quality code.

From the flake8 manpage:

flake8 is a command-line utility for enforcing style consistency across Python projects. By default it includes lint checks provided by the PyFlakes project, PEP-0008 inspired style checks provided by the PyCodeStyle project, and McCabe complexity checking provided by the McCabe project. It will also run third-party extensions if they are found and installed.

[EliAndrewC]

FWIW, we're already using pep8 (https://pypi.python.org/pypi/pep8) for Sideboard itself and for all of the Sideboard plugins that MAGFest writes.

With that being said, I don't have any strong attachment to pep8 and would be fine with switching to something better.

[RobRuana]

Good news! Flake8 includes pep8!

Also, I can't find where in the sideboard project pep8 is being invoked :(

[EliAndrewC]

Whoops, I guess we added that in the past several months where I work. I just opened a new PR that includes pep8 at #62

No urgency on it, but it includes a few other things we'll eventually find helpful.