Rework home page

[bmesuere]

Right now, the home page contains

• A list of course cards for the courses you're subscribed to (grouped by AY, potentially with favorited on top)
• General stats like the number of submissions and solved exercises
• A list of upcoming deadlines over all courses
• A list of recent exercises over all courses

The list of courses is the most prominent, but might not be ideal for all users:

• Some users have a lot of courses (e.g., @pdawyndt has around 60), many of them not super relevant to show on the home page.
• Quite a lot of users only have a single course. Here, a lot of space is wasted and the home page doesn't show a lot of extra things.

In addition, we have a lot more data. The course cards now show some key numbers (submissions and users for teachers, submissions and solved exercises for students), but are they the most relevant? For teachers, maybe submissions in the last week is more relevant?

We added a lot of new features to Dodona over the years. Some of them could be added to the home page more prominently:

• Notifications
• (Open) questions (especially for teachers)
• Ongoing grading sessions (for teachers)
• Grading results (for students)

(Right now, this issue isn't super actionable, but since I wanted to give it a priority, making it a discussion was not an option)