JSONSerializer compatibility for Python 3 bytes

* Update tests `FakeResponse` for Python 3 using `six`
* Update `JSONSerializer` to decode utf-8 before it loads it
* Update .gitignore
* Some too long lines in Django tests

Related issue: #14 
@socketubs if it's not directly referenced, that's an even better argument for it not belonging here. Also, these files are already ignored inside the `tests/` directory, which makes me wonder if you're not running coverage from the wrong location.