Disable 'Ik heb deze stap volbracht' if unauthenticated

[maxvisser]

Description

When a user is not authenticated he can't submit a step as accomplished.

Defintion of done

• [x] Disable button (make it grey) when not logged in.

[KarafiziArtur]

https://github.com/local-motion/onboarding-web/pull/406