Navbar breaks pre-app setup layout

[orenyk]

Since the navbar calls can? :manage, Reservation and CanCanCan checks for AppConfig.first.enable_guests in ability.rb, we get a NoMethodError when rendering the "your app is not set up yet" page. We should either return false unless AppConfig.nil? at the start or check for if AppConfig.first && AppConfig.first.enable_guests to prevent this.

[orenyk]

This ties in nicely with #1092