Leaderboard

I implemented a leaderboard. This seems the obvious next thing to implement after implementing a score. It allows the users to compete among themselves, and to track their own progress.

The leaderboard ranks the top users by score. It lists the top (by score) 100 users who have more than 10 judged wagers. This limit is to prevent the leaderboard from being dominated by users who perhaps made all of one prediction on PredictionBook, and happened to be correct in it. Those on the leaderboard need to have earned their scores in a  consistent fashion, so to introduce a minimum of that, I established this criterion for eligibility to the leaderboard.

To fit the leaderboard link into the nav-menu header, I needed to slightly cut the padding on the nav-menu links. Cutting it down to 19px (from 20px) would have been enough, at least for users with short usernames, but not only did it look crowded, but a long username would have extended the width of the user-links panel enough to cause conflict.

Therefore, I cut the padding down to 14px. This looks a lot nicer, and actually less crowded, as the nav-menu is not right up against the user-links. Also, it avoids the problem of long usernames causing conflict.

I hope that my code this time fits a bit better stylistically; I did my best to follow the style guidelines you gave last time.
This is actually getting 100 users from the database first, then sort them on score. 

I think the right logic should be:
1. get all users
2. sort them
3. get the first 100