Symfony Authenticated through Code Igniter

This is against the Ilios3 branch and allows symfony to check code igniter sessions and use them to authenticate users.  Added configuration option which need to be set to match code igniter options (session_name, encryption key, encrypt cookies).
Created a new namespace LegacyCI which we can use to put all the code in that can go away once v3 is done.
Broke out a bunch of stuff into the Utilities class for testability.
Official credit to @stopfstedt who figured out the way to read CI session at the code jam.