The Cool Levels algorithm should have a heavier emphasis on the date of publish

[turecross321]

Right now, the Cool Levels section can show levels that are many months old. This shouldn't be happening since Cool Levels is meant to contain the most popular *new* levels. A simple way to fix this would be to only show levels that were uploaded in the past week.

[TorutheRedFox]

or create an internal list sorted by date published, and mark the levels with an index that's too high to be removed from the list returned to the game so that if there's low publishing traffic, cool levels won't go empty