WSAPI CHANGES in preparation for new UX flows, specifically where you provide a password AFTER verifying emails.

  * stage_user no longer takes a password
  * after calling stage_user, you can poll status with user_creation_status
  * instead of 'prove_email_ownership', you call 'complete_user_creation' and provide a password
  * add_email is now 'stage_email'
  * after calling stage_email, you can poll status with email_addition_status
  * instead of 'prove_email_ownership', you call 'complete_email_addition' and provide a password
  * stage_* and complete_* calls are POST
  * *_status calls succeed continuously (not only once)