Broadcast to notify all and keep track of responses on item level

[bonndan]

As a user in the role of an architect or security responsible I want to notify all system owners of important events (e.g. security issue like faisalman/ua-parser-js#536 (comment), infrastructure changes having big impact ...) and keep track of the responses (fullfilled? does not apply etc). I cannot reach all owners directly via usual communication since the list is most likely incomplete and outdated and it is not guaranteed to get feedback from all participants or all systems.

requires #601 #746