Add session handling to roadrunner symfony bridge

[alexander-schranz]

Fix parts of #46

The session still have the following problems::

• Invalid session cookie maybe returned when session is not written when nothing was changed
• Session cookie not deleted when not longer valid

[GrahamCampbell]

Why are we using PHP's built-in sessions? In particular, these won't work across multiple servers.

[alexander-schranz]

Symfony uses this also when used Redis or other Session handlers all are calling that method to get the session_id thats why I call it here. I was afraid accessing again the session a new session start is trigger so I did directly access the session_id like here:

https://github.com/symfony/symfony/blob/bbb0a694fbbd5a527b2236636271a47122b5d47c/src/Symfony/Component/HttpFoundation/Session/Storage/Proxy/AbstractProxy.php#L78

[alexander-schranz]

But there are still open problems, so this is still WIP. Have a look at #46 for which things are currently not resolved.

[alexander-schranz]

As described in the issue alternative solution would be which I personally would prefer that maybe symfony add an option to write the cookie at: https://github.com/symfony/symfony/blob/bbb0a694fbbd5a527b2236636271a47122b5d47c/src/Symfony/Component/HttpKernel/EventListener/AbstractSessionListener.php#L110 to $request object this would make less problems for us.

[Nyholm]

Feel free to create a new private method or two

[Nyholm]

Thank you.

Let's merge this and handle the other issues in a separate PR.