When a user with no account tries to login using GitHub/Google auth
they are given an option to register. If the user chooses to
register, a mail is sent for verification and the user has to continue
registration as if they signed up using email. This is confusing and
a bit annoying, so instead of sending email I have changed the
procedure to just redirect to /register where they can start
registration over and proceed normally.
An ideal implementation for this would be to just allow users to
continue registration without email or going back to register.
[greg: tweaked to keep existing user-facing text]
This cleans up the styling of the page by adding the white box
around the text content, and by making the header the same
`.get-started` class as other headers in the portico-signup group.
These handlers will kick into action when is_signup is False. In case
the account exists, the user will be logged in, otherwise, user will
be asked if they want to proceed to registration.