Comments icon colored with no new comments

[fosterfarrell9]

It appears that #515 contains a bug: In production I just posted an answer to a user comment on one of my media, and now I have a yellow comment icon in the navbar indicating that there are new comments, while clicking on the icon shows there are none:

There is no way to decolor the yellow icon (only waiting until someone posts a new commmment somewhere and the clearing all commments). This is actually something we wanted to avoid in #515 but for some reason, it does not work.

[fosterfarrell9]

I can reproduce it in development. Starting scenario: Teacher has no unread comments. Student posts new comment for a medium that does not have a comment yet (I could not reproduce it with a medium that had previuos comments). Teacher's new_comment icon in the navbar turns yellow. Teacher replies to the comment. Then Teacher clicks on the yellow new_comments icon and finds that it does not show anything.
This is actually pretty much a standard scenario, I wonder how we missed it at the time.

[fosterfarrell9]

A quick inspection of the code in comments_controller.rb shows that at no point in the workflow described above the unread_comments flag for the Teacher user is set to false. Probably one should do that around line 218. For the corresponding check we have to incorporate all threads, not just the one considered in the comments_controller#create action.

[fosterfarrell9]

Closed via #585, #587, #594.