Cookbook deprecation emails

:fork_and_knife:

This emails the cookbook owner, cookbook collaborators and cookbook followers when a cookbook is deprecated.
One way to be more explicit about who does and does not receive the email is as follows:

```ruby
Sidekiq::Testing.inline! { the_thing }

recipients = ActionMailer::Base.deliveries.map(&:to).flatten.sort

expect(recipients).to eql(users_to_email.map(&:email).sort)
```