fix: Fix notifications of type "submitted" not being read

[GabrielCWT]

Currently the notifications are not marked as read for type: submitted. When the grading is published, be it manually or automatically, the notification will be marked as read. The grading notification should also be marked as read when the submission is unsubmitted.

I feel that notifications should signify that there are things to be done on the grading page. This solution resolves this bug of there being "things to do" even though there aren't any.

[coveralls]

coverage: 94.365% (+0.009%) from 94.356%
when pulling ff7183c on GabrielCWT:fix/publish-notifications
into 2d43f01 on source-academy:master.

[GabrielCWT]

One thing I have noticed today: Paths also create a notification. Would it be a good idea to add a check where if is_manually_graded is true then create a notification, else do not. This is to follow the idea that the todo count is meant to be for things the staff needs to do in the grading tab.

Furthermore, there is no way to resolve the todo for a path since it is autograded and autopublished

[RichDom2185]

One thing I have noticed today: Paths also create a notification. Would it be a good idea to add a check where if is_manually_graded is true then create a notification, else do not. This is to follow the idea that the todo count is meant to be for things the staff needs to do in the grading tab.

Furthermore, there is no way to resolve the todo for a path since it is autograded and autopublished

This can be a separate issue + PR, thanks!

[RichDom2185]

LGTM, thanks!