Pagination-related theme adjustments:

 * "Clean" URL schema for index pagination.
 * Put the page number and the category name in the <title>.
 * Correct the layout of next/prev links on article pages
   to match that on index pages.
Correct slug for Uncategorized.
Explode media/.

Images and so on are now stored in a subdirectory next to the document they
belong to.  A number of stale or never-used items have been deleted.
Also, all PNGs have been optimized.