feat: Implement `UserRepository.updateSelf`

[apomalyn]

As a developer, I want an method to easily update the signed in user.

Requirements

• Implement UserRepository.updateSelf(User updatedUser, [Map<String, dynamic> extra]), it should
  • update the current user
  • update the local database
  • call the API to update the user

What needs to be done

• Implement UserRepository.updateSelf(User updatedUser, [Map<String, dynamic> extra]), it should:
  • do nothing if there is no user signed in
  • store the current User.last_update as last_update_received in the shared preferences
  • update the current signed in user
  • update the database
  • if display name changes:
  • update the FirebaseUser (doc)
  • call the API to update the user (API #24) passing last_update_received and if necessary update the user again

Dependencies

Child of #130

Depends on:

• 135

• API #24

Dev notes

• Firebase update user documentation