Updated UI and singleton services

[tbeidlershenk]

Changes

1. Updated AuthService by making it singleton and to correctly update Firestore with user documents
2. Added a new data model AppUser to match a user document in Firestore
3. Created a singletonFirebaseService where we should put all related Firestore calls
4. Created a singleton DataService that stores the current lost and found items so we can access from anywhere in the app
5. Updated the UI to use the google_nav_bar package in a new HomePage class that manages all routes in the app, both existing and to be implemented (chat, profile page) and moved the StreamBuilder listening to this page from MapPage
6. Updated route.dart and other files as needed
7. Slightly changed the project folder structure to be more meaningful

Notes

Too many changes bruh please pull and test this Jeff!!! One note I wasn't able to get it to auto update the map when submitting a post which is weird because I think the StreamBuilder should pick up on this but idrk. It does refresh if you physically refresh the page by navigating away then back.

[jeffzheng13]

Pull request not being accepted at the moment. There seems to be some functionality issues at the moment. (Testing on dev db)

My observations:

• Marker design denoting lost and found items not displaying. Displaying a default red map marker icon.
• Unable to add items after clicking submit even after refreshing
• Found items not showing on map
• Logging in does seem to work and create a user.

My suggestion now is, are we able to take one push at time and test? That way we can pinpoint single issues. Right now there's too many things causing errors that I would like to take it one adjustment at a time.

[jeffzheng13]

Appreciate all the work you're putting in @tbeidlershenk👏.

Observations:

• Clicking on map to create a listing, but then exiting leads to nav bar disappearing
• Clicking submit twice while on listing, results in there being two entries in db
• Unable to sign in via a google account (i registered with google and it takes me to log in page but unable to get to map page).
• Logging out should take you out of app completely, but clicking on back arrow takes you back to the map.

[tbeidlershenk]

Closing as we won't be merging this but will still be referencing it