Harden SSL Configuration

As noted in issue #103, our SSL configuration is currently insecure.  Specifically, aNULL ciphers must be excluded in our configuration.  Along with ssl_prefer_server_ciphers (which we have already set), this should protect us from exploits similar to the BEAST attack.  Including SSLv3 seems to be fine according to resources I have skimmed.

That said, I am not fluent with SSL certificates and would like input from @igalic and others on the topic.  

References:
* http://nginx.org/en/docs/http/configuring_https_servers.html
* http://www.hybridforge.com/blog/nginx-ssl-ciphers-and-pci-compliance