improve and update server configuration documentation (rebased from develop)

Makes a start on the work for https://trello.com/c/Gpwp1WkC/188-improve-server-config-docs and removes some information about both OMEIS archeology and, from https://trello.com/c/avvIvqCk/67-5-0-3-follow-up, our long-neglected OpenGL clients.
--rebased-from #948
@mtbc I'd like the "minimum" specifications to also only include security-supported versions; since this the the minimum for a server deployment, people should not have an unreasonable expectation of being able to deploy on a known insecure and unsupported system; we might be a bit less restrictive on the client side, but even there be clear about it being the minimum rather than recommended.