Provide instructions and a requirements list to quickly start the sample application. Related to #4291173

Use the pyramid session object as the cubiweb session.data (needs a patched cw 3.19) Related to #4291173

Add comments on parts we want to reconsider later Related to #4291173

Skip core_handle, add a context manager to handle cubicweb errors The context manager is also used to catch errors in render_view. It handles the 'external' errors raised by cubicweb code. The more internal errors, the one that should occur only in url resolving and cubicweb controllers, are handled directly in CubicWebPyramidHandler. ValidationError is handled by CubicWebPyramidHandler for now, but should probably be handled by cw_to_pyramid Related to #4291173

Documents dependencies on a ubuntu system Related to #4291173

Use short-lived cubicweb sessions to let pyramid actually handle the web sessions Related to #4291173

Isolate the default handler and extend its role The handler now does the job of CubicWebPublisher.main_handle_request() and calls CubicWebPublisher.core_handle(). Instead of using config.add_notfound_view, a catchall route is defined and the handler plugged to it. Related to #4291173

Add a basic sample application Related to #4291173

Integration pyramid and cubicweb authentication. We use pyramid sessions to store the cubicweb sessionid so we can reuse it when needed, or regenerate it if it was lost. The cubicweb sessionid is obtained from a login in the repo OR directly from the user identified by pyramid. Related to #4291173

[doc] Escape _ in README.md So that the Markdown is okay.