Hash emails

[wmurphyrd]

No more storing plaintext emails.

• Save an sha256 hash of the email,
• Hash the input email before querying when doing password reset
• Use the input email as the address for the email
• Includes migration to hash all existing emails
• Adds an explanatory note to the registration form with configurable link to email opt-in

[wmurphyrd]

@quinn-madson word of warning on this one - this is the first PR with a new migration since I changed the setup to run migrations automatically on startup, so backup that local DB before testing this one