Will/vagrant like prod

Update the Vagrant instance to use gunicorn, nginx, mysql, memcached, and upstart.  The VM now runs all services in the background, including Celery workers and the Celery Flower monitoring tool.  The README describes how to use the VM in more detail.

I've also updated the URLs to serve workbench from `/` instead of `/workbench`.

Related PRs:
* https://github.com/edx/ease/pull/57: EASE is still missing some requirements when installing from setup.py.  Once this PR gets merged, it should work correctly.

* https://github.com/edx/xblock-sdk/pull/14: Gunicorn + MySQL with repeatable read sometimes breaks workbench.  This PR should fix the issue, but will require uninstalling and re-installing the XBlock SDK.

@stephensanchez