Table: toggle changed self.update() fixes #5839 - toggle breaks table priority hiding

This should fix #5839 - columns stay hidden when shrinking and resizing the browser window. 

With the fix, showing and hiding of columns is purely done based on priority-CSS. Only when the user manually toggles a column it's `jqmData(cells)` which now also includes the header cell itself will be locked to `show()/hide()`. 

With the fix, there is also no more need for `ui-table-cell-hidden` and `ui-table-cell-visible`.

Hope this is the correct branch...

[Sample page with fix](http://bit.ly/17WKxop)