We don't guess the current profile anymore if the value of the profile === -1
Also sets $this->scoped for all ScopingNoticeStream inheritors, which just
like in an Action can be null if we're not scoped in any way (logged in).
For those pages where threading is important, we now have an extra filtering stream
class to skip stuff in conversations that have "already" been seen.
Added filtering code so that notice streams check notice scope.
Added new class to implement filtering a stream, FilteringNoticeStream.
Added a subclass that does the logic for checking Notice scope.
And made all the streams use ScopingNoticeStream.
