[REF] tablesorter: use id attribute to select columns instead of column index to avoid duplicating smarty template logic for which columns to show (inspired by a conversation with Jonny while hanging out in Covent Garden). Other minor cleanup as well.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@53180 b456876b-0849-0410-b77d-98878d47e9d5