Per-package notification

While it works nicely to send emails to the people directly responsible for breaking a build, a second notification channel should be added. Some way each package can notify either on IRC or a shared email address.

No files, tests, or entry points are identified in the issue, so start by surveying the packaging notification flow and how package ownership is configured. Done means each package has a documented way to notify either an IRC channel or a shared email address, in addition to direct build-break notifications.

Written by the indexing model from the issue text.