Cookbook notification emails should be about the updated version.

:fork_and_knife: Currently when a cookbook is updated a notification email goes out with info for the latest cookbook version. This works in most cases but there is a chance that the email will not actually pertain to the version that triggered it. This changes the mailer so it accepts a cookbook version, allowing each email to pertain to the exact version that was updated.

Closes #847.
These params are in the reverse order from their definition in `cookbook_mailer.rb`