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`
Still seeing the following error after pulling down the most recent changes on this branch:

```bash
$ git pull https://github.com/maurizi/nyc-trees.git django-js
From https://github.com/maurizi/nyc-trees
 * branch            django-js  -> FETCH_HEAD
Already up-to-date.
$ git status
On branch maurizi-django-js
nothing to commit, working directory clean
```

**Error output**:

```bash
TASK: [nyc-trees.app | Create static files and run collectstatic (development)] ***
failed: [app] => {"changed": true, "cmd": ["npm", "run", "build-debug"], "delta": "0:00:02.155363", "end": "2014-12-01 00:04:22.007049", "rc": 1, "start": "2014-12-01 00:04:19.851686"}
stderr:
npm ERR! nyc-trees@0.0.0 build-debug: `gulp build --debug`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the nyc-trees@0.0.0 build-debug script.
npm ERR! This is most likely a problem with the nyc-trees package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     gulp build --debug
npm ERR! You can get their info via:
npm ERR!     npm owner ls nyc-trees
npm ERR! There is likely additional logging output above.
npm ERR! System Linux 3.13.0-32-generic
npm ERR! command "/usr/local/bin/node" "/usr/local/bin/npm" "run" "build-debug"
npm ERR! cwd /opt/app
npm ERR! node -v v0.10.32
npm ERR! npm -v 1.4.28
npm ERR! code ELIFECYCLE
npm ERR!
npm ERR! Additional logging details can be found in:
npm ERR!     /opt/app/npm-debug.log
npm ERR! not ok code 0
stdout:
> nyc-trees@0.0.0 build-debug /opt/app
> gulp build --debug

[00:04:21] Using gulpfile /opt/app/gulpfile.js
[00:04:21] Starting 'build'...
[00:04:21] Starting 'clean'...
[00:04:21] Starting 'copy'...
[00:04:21] Finished 'clean' after 11 ms
[00:04:21] Starting 'browserify'...
[00:04:21] Starting 'sass'...
[00:04:21] Starting 'vendor-css'...
[00:04:21] Finished 'copy' after 42 ms
[00:04:21] Finished 'sass' after 15 ms
[00:04:21] Finished 'vendor-css' after 13 ms
[00:04:21] Finished 'browserify' after 617 ms
[00:04:21] Starting 'copy-dev-assets'...
[00:04:21] 'copy-dev-assets' errored after 8.48 ms
[00:04:21] Error: EACCES, mkdir '/var/cache/nyc-trees/static/js'
[00:04:21] 'build' errored after 640 ms
[00:04:21] Error: [object Object]
    at formatError (/var/cache/nyc-trees/node_modules/gulp/bin/gulp.js:169:10)
    at Gulp.<anonymous> (/var/cache/nyc-trees/node_modules/gulp/bin/gulp.js:195:15)
    at Gulp.emit (events.js:117:20)
    at Gulp.Orchestrator._emitTaskDone (/var/cache/nyc-trees/node_modules/orchestrator/index.js:264:8)
    at /var/cache/nyc-trees/node_modules/orchestrator/index.js:275:23
    at finish (/var/cache/nyc-trees/node_modules/orchestrator/lib/runTask.js:21:8)
    at cb (/var/cache/nyc-trees/node_modules/orchestrator/lib/runTask.js:29:3)
    at finish (/var/cache/nyc-trees/node_modules/run-sequence/index.js:48:5)
    at Gulp.onError (/var/cache/nyc-trees/node_modules/run-sequence/index.js:55:4)
    at Gulp.emit (events.js:117:20)

FATAL: all hosts have already failed -- aborting
```