[ENH] Add column selector button which allows for hiding and re-showing columns on the fly, and to prioritize them to determine which columns disappear first when the browser is too narrow. Some other minor cleanup as well.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@53186 b456876b-0849-0410-b77d-98878d47e9d5
tablesorter: update to latest version 2.18.3

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@53187 b456876b-0849-0410-b77d-98878d47e9d5