Prepare for navigation

This IoT app has two top-level screens,
along with the setup flow. Define these 
route names as constants so that they can
be referenced within code.

The home and settings screens are referenced with
static names. The setup flow pages, however,
use two paths to create their route names: 
a /setup/ prefix followed by the name of the specific page.
By combining the two paths, your Navigator can determine
that a route name is intended for the setup flow without
recognizing all the individual pages associated with 
the setup flow.

The top-level Navigator isn’t responsible for identifying
individual setup flow pages. Therefore, your top-level
Navigator needs to parse the incoming route name to
identify the setup flow prefix. Needing to parse the route name 
means that you can’t use the routes property of your top-level
Navigator. Instead, you must provide a function for the
onGenerateRoute property.