Re-work top-level state management and navigate in response to notifications
This MR includes the changes necessary for the second half of #6 (closed).
- Moved the top-level view state for the app out of random SwiftUI
@State
vars in Views, and into a newViewState
class that lives inside theCirclesApplicationSession
. - Make the current application session accessible as a static singleton object of the class
- Reach out from the app delegate to find the current application session and tell it to navigate its view state to the given room id when the user taps a notification