Add config settings for a 'busy query notification' system
Add a class whose job it is to send notifications once we receive enough events to require a query refresh for a particular product
Add an interface for the query notifier
Add a pipeline stage to pass events along to a notifier
Add the notifier stage to the event pipeline (but it's not initialised yet, so nothing will happen)
Create the query notifier and properly set up the stage
Merge branch 'feature/QueryNotifications'