support for proxy_prefix

[abretaud]

Askomics docker should have a PROXY_PREFIX env var that make it work properly when it runs behind a proxy.
E.g. when it's accessed at http://somewhere/gie_proxy/askomics/ when used as a galaxy IE behind an nginx proxy

The current workaround is to add a specific proxy_pass/proxy_redirect rule in the nginx proxy. This is ugly.

[xgaia]

Not the right repo.

https://github.com/xgaia/docker-askomics-virtuoso-ie

[abretaud]

ahah leaul