feat: Implement sign out

[apomalyn]

As a user, I want to be able to log out from the application whenever I want.

Requirements

• In the settings, add the "Account" section at the top of the screen
  • add a "Sign out" that, when pressed, sign out the user. This can only be accessible when a permanent account is used (no anonymous)
• Implement the UserRepository.signOut()

What needs to be done

• Update the UserRepository.signOut() function to:
  • be usable only when the user isn't anonymous and is logged in
  • log out the user of the Firebase
  • clear the instance of the user
  • clear the user and knowledge level in the local database
• In the settings/settings_view, add:
  • a section "Account" at the top of the screen
  • under the previously created section add a "Sign out" button
  • those should be available only if the user connected isn't anonymous
• In the settings/settings_view_model, add an onSignOutPressed that:
  • calls UserRepository.signOut()
  • redirect to the Landing page

Dependencies

Child of #130

Depends on:

• 135

• 137

• 138

[Adaendra]

@apomalyn Comment ça se passe pour un flow anonyme qui se déconnecte et qui se reconnecte en anonyme ? Techniquement ce sont deux utilisateurs différents, donc on doit recommencer de 0. Est-ce qu'on veut ajouter un message d'avertissement pour prévenir l'utilisateur si il veut se déconnecter ? ou souhaitons-nous migrer les données vers le nouveau compte ?