Handle disabled account registration

[jacobtread]

Description

Once the server implements https://github.com/PocketRelay/Server/issues/37 the dashboard needs to have a way to determine that account registration is disabled in order to hide the UI for creating accounts (UX improvement)

Dependent

• Requires disabling registration to be implemented https://github.com/PocketRelay/Server/issues/37

Checklist

• [x] Clients can detect that registration is disabled and the create view is disabled