After a topic is closed, the assignment is not deleted but becomes
inactive. When this happened, it was not removed from the assignments
count or list.
Change `topic_id` to polymorphic approach (In the next step we will allow assigning to individual post)
`topic_id` column is still used for efficient display of assigned users on topic list (to avoid scanning posts)
Ability to assign groups.
To assign group, user must have a right to send a message to that group.
In addition, 2 jobs were introduced, - AssignNotification and UnassignNotification to inform interested users in the background about the new assignment.
This significantly reduces the amount of logic we need to carry in the discourse-assign plugin. One side effect is that I had to rename the 'q' parameter to 'search', so that it matches core's implementation.
Rafael dos Santos Silva
Bianca Nenciu
Krzysztof Kotlarek
Jarek Radosz
David Taylor
Ahmed Gagan