Fixed EZP-20805: SiteAccess and other request attributes lost in sub-requests

This PR fixes how siteaccess and other request parameters are retrieved/injected when in a sub-request (either inline, ESI or Hinclude).

Since migration to Symfony 2.2, those critical information were actually lost and default siteaccess was always used in sub-requests.
This PR serializes the information in the *fragment* path so that they can be safely retrieved by request listeners.

Tested with inline, ESI and Hinclude sub-requests (and also mixed combinations)