When showing challenges in Leaderboard, distinguish finished from active challenges

[mvexel]

In the leaderboard, you can inspect the top users' top challenges. Some of these may be finished, others active. Both are clickable. We should either distinguish (color? symbol?) the finished challenges from the active ones, or make the finished ones non-clickable. I prefer the former since there's still useful information to be seen in the challenge browse screen.

[raphaelpe]

I prefer to distinguish by color, red for the finishes, green for the assets and yellow for the ones that are in progress