Replace session sharing to use phpbb3 only for authentication

[MasterMind2k]

Sharing sessions from two separate systems is not a good idea.

We need to refactor the whole session layer, it should not be shared.

Scope:

• use sid and PHPBB3 cookie only for verifying user was authenticated
  • please note, session cookies may not be available
• store in it's own session cache (use the available Cache object, it could be separate)
  • we can talk offline for some ideas how to set-it up