Wipe and install Ansible roles

The previous method to install dependent roles was not accounting for
scenarios where a role existed on the file system, but needed to be
updated. This changeset removes all `azavea.*` roles and then reinstalls
them.
Use latest `azavea.nginx` ansible role
Merge pull request #39 from RickMohr/update-azavea-nginx

Use latest `azavea.nginx` ansible role
Merge branch 'feature/wipe-and-install' into develop
Bump version of Node.js role

Attempts to resolve #41.
Wire up the database

This changeset connects the Django application (running on `app`) to the
PostgreSQL database (running on `services`). The Django application is
setup to pull database settings in from the environment and `envdir` is
used to populate the environment.

Example usage:

```bash
$ vagrant ssh app
vagrant@app:~$ envdir /etc/nyc-trees.d/env /opt/app/manage.py runserver
```

Attempts to resolve the following issues:

- https://github.com/azavea/nyc-trees/issues/28
- https://github.com/azavea/nyc-trees/issues/31
- https://github.com/azavea/nyc-trees/issues/35
- https://github.com/azavea/nyc-trees/issues/36