Do not confuse workers as guest if guest_only mode is enabled
Whenever guest_only was enabled in the settings, the controlled view
would automatically 'login as guest' before doing anything which caused
a worker to always appear as a guest (no Logout option and no access to
Private projects).
This would also happen if you access the website (which logs you in as guest
automatically) before logging in as a worker since the cookie that identifies
you as a guest will remain there.
By preventing the login as guest to being called if we're already logged in
and removing the 'guest' cookie when a worker successfully logs in,
we can restore the proper behavior of workers.
Fixes issue #29