Update email validation rules to disallow the percent character (e.g.
`foo%bar@gmail.com`) and names ending with a period (e.g. `foo.@gmail.com`).
Names ending with a period are invalid according to the RFCs and cause
`Mail::Address.new` to raise an exception.
The percent character is technically legal, but only one email used it
and it was probably a typo.
Try to automatically fix various kind of typos and common mistakes in
email addresses when a user creates a new account. It's common for users
to signup with addresses like `name@gmai.com`, which leads to bounces
when we try to send the welcome email.
