Fixed testing, fixed python3 compatibility, added classifiers for PyPI

- Made it possible to run `python manage.py test` and get passing tests
- Added a `.travis.yml` file to enable Travis CI builds
- Fixed Python 3 compatibility without compromising Django 1.4 compatibility
- Added trove classifiers to `setup.py` for PyPI
The `ENV` column in Travis is a little bit hard to read, let's change this part to:
```yaml
env:
    - DJANGO="django==1.4"
    - DJANGO="django==1.5"
    - DJANGO="django==1.6"
    - DJANGO="django==1.7"
```