Users can delete their account and expunge all of their data

[mmcknett]

• [ ] There's a dropdown next to "Log Out" that contains "Delete Account"
• [ ] A confirmation dialog makes it clear that all data will be deleted and that the action is irreversible.
• [ ] All logs for a user and the user account are removed from firestore and firebase auth
• [ ] There's a cypress test for the flow that...
  • Exercises the UI
  • Verifies that the account is removed from firestore
  • Verifies that the account has been deleted from firebase auth