confirmation changes for better user friendliness

This address the concern that when you click an already confirmed email confirmation link it just says "token invalid". Now it:

* Prompts the user to enter their email address again on the event of error with some quick text. (If the token is expired, there's no way to extract it automatically. It already asked for email, but now there's an explanatory sentence.)

* If they enter an email which is already associated with a confirmed account, it redirects them to log in with a message saying what to do and auto focuses the password instead of the email, saving them from typing it twice.

* Otherwise, the same behavior remains.