make sure dragdealer refreshes wrapper offset before dragging
don't use TD for focus because it scrolls the window; use focusCatcher (DIV position: fixed) instead
fix tests after last TD focus changes
fix test that never really worked correctly
last change broke chainability
bugfix: currentRowClassName and currentColClassName not kept while scrolling (#455); refactor Walkontable selection
after last fix to core `getColHeader` method, this part here got broken