Extension requests should not appear in task inbox until there is a submission

[jakerenzella]

Currently the inbox can get spammed with notifications after many student's apply for extensions, even though there are no submissions. They will stay in the inbox until responded, forcing the tutor to make an action. Without a submission

If there's a submission which is late, and there's a request then we can place it in the inbox. If the submission is early then it shouldn't matter anyway. If the task is marked while a pending request exists then we should delete the request as it wasn't needed.

Thoughts @macite ?

[macite]

We should review this whole process.