nginx reverse-proxy config needs to be updated

[hughrun]

Describe the bug
The Reverse-Proxy config:

• doesn't allow /flower to be accessed
• doesn't use the latest restrictions on non-image files being served from /images/
• doesn't appear to suppress logging of requests to /static/ like the core config does

To Reproduce
Steps to reproduce the behavior:

1. Use a reverse proxy
2. Be frustrated and possibly run an insecure instance

I think we probably need to update both the production nginx config file and the reverse-proxy documentation on the docs site, however I'm not very confident with nginx config and haven't found much in the way of helpful documentation other than the most basic reverse-proxy setup.