Show list of unadded courses

[npalladium]

Some courses are not added to the timetable as they do not adhere to a proper slot. Currently the extension only displays a warning about them. It should also write them permanently to the Timetable page.

[RachitKeertiDas]

Now that we have started displaying legends for courses in the timetable page, I think we can just add it to the legend, but not show on timetable?