Unconfirmed accounts allocate a username

[simonbaird]

Not sure what to do about that, but the problematic user story goes like this:

• Signup with your preferred username but accidentally put a typo in your email address
• The bad email address means the account can never be confirmed
• The unique username constraint means the username is forever considered "taken"

Ideas:

• Make the username unique across confirm accounts only... but this might result in usernames being rejected once an account is confirmed, which would be hard to handle.
• Ask user for their username only after their email is confirmed... Could be done with a new dedicated form, or just a suggestion for user to go set their username if they wish.
  • Suggestion could be implemented as a permanent "hint", particularly for anyone with a hub site and no username.