Add support for Gunicorn/Nginx

This changeset makes Gunicorn the application server for Django across
environments. In addition, Upstart handles launching the Gunicorn worker
pool and Nginx reverse proxies requests to it.

It is also important to note that when the application is provisioned in
the development and test environments, the Gunicorn `--reload` flag is
used. This provides automatic Gunicorn worker reloads when code changes
occur. I tested application reloading by making source code changes via
the Vagrant shared folder and worker PIDs changed as expected.

For more discussion, see: https://github.com/azavea/nyc-trees/pull/71
Enabling debugging support in development

In addition, I set `timeout` to 30 minutes and lowered it to 60 in the
`else` because the ELB terminates requests at 60 seconds anyway.
Remove references to `runserver`
Move gunicorn configuration to config file

This will make it easier to use the same config in multiple places
Add proof of concept script for gunicorn debugging
static -> collected_static (for now)
Move scripts to folder
Merge pull request #73 from azavea/feature/unicorn-nginx

Add support for Gunicorn/Nginx
Activate admin site
PR Fixup: Pull out admin docs?
PR Fixup: drop relative imports
PR Fixup: Give better overview in admin-checklist
PR Fixup: delete URL stubs for known admin pages