ERP5: add the ability to run in WSGI mode

This is a first step, just to switch to WSGI. Using Waitress as WSGI server may be temporary, because it lacks SSL support and later we'll want to have IPv6 SSL sockets. So we'll either implement the SSL layer ourselves or switch to something else like gevent.

Actually, we started with gevent for SSL but it has an issue that may be hard to solve.

zope.globalrequest is a backported dependency from recent Zope.