Enable user to delete all data and create new password

[j-berman]

Overview

As proposed by @alexcnichols in #59, in addition to Userbase's current forgot password mechanism (#103), it would be a nice feature to allow users who lose their password to delete all their data and create a new password.

Proposed Implementation

• A user must have an email saved on their account.
• A developer can call a new Userbase SDK function resetAccount({ username }) or something similar, which sends a message to the user's email.
• The message will contain a temporary reset password that will expire after 24 hours.
• The user simply has to provide that value as their password to signIn().
• If the user provides the correct reset password to signIn(), Userbase will mark all the user's old data for deletion (to be deleted asynchronously in the nightly purge) then allow the user to sign in normally (& create a new password).

Note, the user's plaintext data (profile + protectedProfile) would not be deleted.