Challenges: reset the score daily

Now that the challenges are coming back to Nevado make the scores reset every day and store old highest scores (previous/week/month/season/all time) separately.

In Hintertux and older versions challenge score stored was all time high and that was quite de-motivating when score achieved was by accident (like edge angle 87 deg and then crashing) and would not be repeated any time soon, if ever. Daily challenge would be fun or if that is difficult to make, then make a button to zero the current score.