Add content QA environments

- Add contentqa_proxy role that allows us to serve the contentqa
  app to the world on port 80 without complicating the
  configuration of our existing API proxy.
- Ensure existence of QA API account
- Add postfix configuration, which will be useful for staging and
  production.
- Add locale configuration
- Change default encoding of PostgreSQL database
- Change the assignment of BigCouch nodes and ElasticSearch cluster
  names so that they're limited to one server for contentqa.
- Add lines in .gitignore for other inventory files for
  production and staging