initial doc on base crate containers

This will serve as the working pull request for base crate containers.

Base containers provide pre-packages functionality such as Redis, Nginx, uWSGI, etc.  Crate will utilize cloud-init to provision the container.  From those, users can clone, edit, repeat as desired.

Core Base Containers

* apache2
* graphite
* graylog2
* haproxy
* memcached
* mongodb
* mysql
* nginx
* openresty
* postgres
* puppet (master, dashboard, puppetdb)
* rabbitmq
* redis
* sensu
* sentry
* solr
* uwsgi

These are just the core and will add over time.  These are also managed via Puppet and will be updatable over the lifetime of the container.