Fix for notification/email

- Email sent from ETT did not contain information about what was changed. This
  was caused because we use @package.latest_changes method to obtain what
  changed in the package. Unfortunately, we write to the @package object and
  this alters the latest_changes method output (we write to
  @package.status_changed_at, and therefore latest_changes will return that as
  the latest change instead of status_id, or assignee change, or name change).

- We fix it by calling latest_changes before @package.status_changed_at is
  written to.

- Also some minor refactorings as to how the link in the email is generated.