Use lightweight sessions
Provides a lightweight version of repo.connect() that does not keep track of
opened sessions.
The speed gain on a mostly static front page is about 5%
Warning ! This means that, for now, the "session_open" and "session_close"
hooks are NOT called anymore.
Use 'wsgicors' for CORS handling.
The CW CORS handling (in web/cors.py) is only able to work on cubicweb requests.
When a request is not handled by bwcompat, we need a proper solution.
The `wsgicors` library provides what we need as a wsgi middleware.