* Loop through $UsedCategories to generate filter links and .ghide() and
  .gshow() statements for each tr of the class that matches the category to
  to be filtered. Also allow for Show All.
* As nth-child is used for styling .ghide() and .gshow() natively breaks the
  zebra-striping. This is re-applied in apply_torrent_table_styling().
  The function removes CSS classes rowlight and rowdark with jquery :odd
  and :even CSS selectors Additional CSS were needed as nth-child cannot be
  referenced by .addClass().
* CSS styling for category filter links.