Extracted logout to the login service so the logic can be shared instead
of re-implemented at each stage. For this, the SocialAuthService was
split so the driver management is in its own class, so it can be used
elsewhere without use (or circular dependencies) of the
SocialAuthService.
During review of #4467
Added test and changed logic to properly check the view permissions for
the notification receiver before sending.
Required change to permissions applicator to allow the user to be
manually determined, and a service provider update to provide the class
as a singleton without a specific user, so it checks the current logged
in user on demand.
