Styling: Update to match the same styling as TableTools

- ColVis is in bad need of a big update (re-write). The plan is to
  create a 'buttons' control for DataTables which can be re-used for
  TableTools, ColVis and anything else needing buttons (Editor, button
  based filtering etc), providing a simple single combined interface for
  the buttons. That's post 1.10.0 though as need to focus on that just
  now!