Phase 2: Withings sync update

Relies on: https://github.com/ijustwanttocode/whyeatthings/pull/74

- Health Accounts controller manages the accounts a user has
- If exists, you can import and delete
- If not exists, you can authorize and a credential will be stored from the user.  This logic was removed from the dashboards controller and the import action.
We may want to move this case statement to a factory method that determine what type of service to return. To handle the else we could create an InvalidServiceProvider. This hide the case statement as it gets bigger from the controller.