Nginx doc

This PR review OMERO.web deployment for various purposes. Basically it split instructions for developers and system administrators to not confuse each other.

My only comment is that it is nasty that ```static_url``` doesn't pick up ```force_script_name``` but I have no way of knowing what was set in previous deployment. Either we leave it as it is or doing it in a right way we will need to add instruction to upgrade script as it will break existing deployment scripts
My PYTHONPATH problem only manifests when running web, plus it is fixed now.

This is a docs PR, I did my actual test on develop. If you want me to test something else then you will have to specify the branch.