add optional nginx configs to make more secure

Add back some items removed in https://github.com/gitlabhq/gitlabhq/commit/8aff39a6d0a63e904ada910900ee07a1c3190a9d but makes them optional so they can be ignored if you want a simple setup experience.
@bbodenmiller I politely disagree (see http://en.wikipedia.org/wiki/Online_Certificate_Status_Protocol Criticisms) and hope that we can merge it with the non-recommended status. If you want a broader opinion I can ask the GitLab core team for a vote.