Add authorization steps for PAUSE accounts

[preaction]

When a user is registered (#13), we should prompt them to authorize their PAUSE account. Users with authorized PAUSE accounts will be allowed to mark incoming reports as INVALID, and otherwise act as authorities for the distributions they have administrative access to (FIRSTCOME or COMAINT).

The authorization process should generate a token and send an e-mail to <PAUSEID>@cpan.org. The e-mail should contain a link and the generated token. When the user clicks the link or pastes in the token, they should become authorized to the given PAUSE account.