improve and update server configuration documentation

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.
Thoughts on rearranging so Linux is first as a subtle hint that's it recommended over the others?