feat: Implement delete account

[apomalyn]

As a user, I want to be able to delete my account if I wish to.

Requirements

• Implement a button on the settings to delete the account of the user
  • Before deleting the account, user confirmation should be asked
• After deletion, the local storage of user data should be empty

What needs to be done

• Implement UserRepository.deleteAccount(), it should:
  • call the API DELETE /user
  • handle errors
  • remove all user-related data from the local database
  • log out Firebase user
• On settings/settings_view, at the end of the screen, under a "Danger" section, add a "Delete account" button.
  • button should be primary red to indicate the danger to click on it
  • When pressed, a confirmation dialog should pop up
• On settings/settings_view_model add the function that will called when the user has confirmed account deletion. It should:
  • call UserRepository.deleteAccount()
  • on success, redirect to the landing page

Dependencies

Child of #130

Depends on:

• 135

• API #17