Add authorization steps for tester e-mail addresses

[preaction]

When a user is registered (#13), we should prompt them to authorize their tester e-mail addresses. Once a user is authorized to a tester e-mail address, they will be allowed to administer the reports they've submitting, including marking them as INVALID or deleting them (these actions are for future tickets).

Similar to authorizing PAUSE accounts (#14), the authorization process should generate a token and send an e-mail to the given e-mail address. 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 tester e-mail address.