Integrate proof of concept gulpfile into Django project

 - Changes the Django `static` and `media` directories to be inside `/var/www/nyc-trees/`
 - Adds the `static` template filter for converting static file to use their versioned path
 - Fixes a few issues with the proof of concept `gulpfile`
@hectcastro Did you run `vagrant destroy app` beforehand?

The one thing I haven't figured out is how to handle switching between having `VAGRANT_ENV=TEST` set or not.  I can get things to consistently work if you `vagrant destroy` before switching `VAGRANT_ENV` though...