:bug: Existing Twitch Account Association

[ProgrammingByPermutation]

If someone logs into the site without an e-mail address in the User table but they do have a twitch username, the site creates a new entry for that user in the user table.

I don't care about existing duplicates, we can clean those up manually.

If someone tries to log in with their twitch account and we have an existing row for them with no e-mail, we should update that row with the rest of their data.