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
For "25-50" users, do we want to recommend MacOS *at all*?  I'm unsure this could ever be considered suitable for any serious real-world deployment.  There is no suitable Apple hardware for this unless you go to a brand new Mac Pro (in which case it's 10.9), and even then the I/O may be awful for a multi-user application.

Also, for the minimum requirements, do we want to move up to versions which have security support?  So MacOS X 10.8 rather than 10.6 (10.7 is due to be dropped when 10.10 comes out in a few weeks), Windows Vista/7 rather than XP.