Challenges with a list of things should show what's done/left to do.

[DrDraken 481]

For challenges that require doing a series of things, it would be great to be able to select that challenge and see what's left to do.

For example: Do a Grand Prix in 10 different cars.  I didn't just start at one end and work my way through, so I couldn't remember which I had done or not.  Being able to see a list of what had been done would be very handy.