Recent Topics and Best-Of Topics changes

+ Restricted "recent topics" to the past month of activity
+ Changed "best-of" favorite counts to just show a number of tropies
(1-3) instead of the raw count.
+ Refactored hompage/post/page header images to be 3 separate image
files, instead of one large sprite. Only one of these files will ever be
loaded on any given page, so it reduces the total request size.