[ticket/11761] Serve blank file locally in functional test

Example.org no longer serves blank responses, failing functional tests.

this patch creates a  blank file and serve it locally during the test,
instead of hitting the http://example.org servers kindly provided by IANA.

PHPBB3-9733
[feature/session-storage] Move interface functions

Moved interface functions so that they center around
the sql table that they represent. This makes writing
underlying storage easier because the kinds of actions
that you would perform on that data are all under the
same interface.

PHPBB3-9733