Better prioritization of implemented issues (to be closed)

This release provides better visibility of which issues are ready to be closed.

When an issue remains open after its related pull requests have been merged, we now move the issue back to the priority inbox of its assignees with the action close.

This new behaviour allows you to take action on the issue, that is either re-assign it to people which must still do work on it (e.g. end to end testing) or simply close it. No dangling issue due to someone forgetting to close it!

Along with this new feature we now display issues which are currently being implemented by pull requests in the Coming Up tab with the action Wait for PR. This allows you to see at a glance which issues are currently being worked on, but without spamming your actual inbox. As with pull requests, you can see the unified feed of discussions on these issues.