Take FORCE_SCRIPT_NAME setting into account

I routinely deploy Django apps behind a reverse proxy where the root url of the Django app is not "/" e.g.
Public facing server will take requests to http://mysite.com/myapp/ and reverse proxy them to http://localhost:8080/

Django.js does not currently handle this situation ([issue #34](https://github.com/noirbizarre/django.js/issues/34) appears to be related) without having to resort to manually prefix urls with your script name in your js files. For example if my app is hosted at http://mysite.com/myapp/ then `Django.url('home')` will give `"/"` rather than the desired `"/myapp/"`.  This pull request should resolve that.