Fix unicode issue (plus pep8 changes)

@EDITD/hackers I noticed [this](https://app.getsentry.com/editd/drawbridge/group/16182693/) today and thought of throwing a quick fix together.

I believe usage of `str()` should be avoided unless specifically required, as there are many unicode pitfalls in python2 that come from its usage. I have replaced all occurences in this repo with `unicode()`, which should take care of most issues (apart from mislabeling unicode strings containg ascii data and complex stuff like that).

If this is accepted, I will make a new PR for the drawbridge repo to point to the new release as a dependency.