Account management improvements

[rubenwardy]

• [x] Include created_at in User model
• [x] Delete unverified accounts after 24 hours
• [x] Add confirmation page after an email verification is sent. ie: "Check your mail"
• [x] Allow moderators to set email addresses and send password resets at the same time
• [x] Add help page for "can't log in"
• [x] Add email verification expiry