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`
Ok, I can try taking it back out.

I switched `createhome=yes` to `home=/var/lib/nyc-trees` at the same time that I added this, maybe `home=/var/lib/nyc-trees` was enough...