Stashing Katana Auth work
Started a new authentication service to pull auth-related stuff out of UserService.

Also, as a demonstration of a cleaner service layer.
Implemented AuthenticationService.AuthenticateUser
Stashing auth rearch
Moved things over to use UserSession instead of IPrincipal
Moved authentication logic to its own service
Fixed up infrastructure
Switched to default auth cookie name
C is for COOKIE AUTH!