[DEV-2153] Refashion "People" page into a leaderboard.

@mwhansen cr?

The leaderboard template is mostly a copy-paste of the user list page template from Askbot, with some pieces removed and a few pieces that were previously in macros inlined and modified.
The paginator is actually the django Paginator object, not the Page object.  Its object_list is the full queryset returned by get_queryset.  I'll redo the implementation of get_leaderboard_position as suggested, though; it's a cleaner solution.