Add support for installing project dependencies in development

This changeset adds the `nyc-trees.app` role to capture tasks directly
tied to the nyc-trees Django application. The first step is installing
the project's requirements file, and any system dependencies it may
have.
Cleanup Vagrantfile

This changeset cleans up the existing Vagrantfile by:

- Ensuring that methods in a block use the passed variable
- Explicitly disabling the /vagrant share
Merge branch 'feature/django-deps' into develop
Remove Chef service in development

The Ubuntu 14.04 (Trusty) Vagrant box has the `chef-client` service
running by default. This changeset removes the `chef-client` service if
it exists in development.
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